Imperial units

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The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road). Weights and Measures office.jpg
The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road).

The system of imperial units or the imperial system (also known as British Imperial [1] or Exchequer Standards of 1825) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The Imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825. [2] The system came into official use across the British Empire. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, although some imperial units are still used in the United Kingdom, Canada and other countries formerly part of the British Empire. The imperial system developed from what were first known as English units, as did the related system of United States customary units.

Weights and Measures Acts (UK)

Weights and measures acts are acts of the British Parliament determining the regulation of weights and measures. It also refers to similar royal and parliamentary acts of the Kingdoms of England and Scotland and the medieval Welsh states. The earliest of these were originally untitled but were given descriptive glosses or titles based upon the monarch under whose reign they were promulgated. Several omnibus modern acts are entitled the Weights and Measures Act and are distinguished by the year of their enactment.

Winchester measure is a set of legal standards of volume instituted in the late 15th century (1495) by King Henry VII of England and in use, with some modifications, until the present day. It consists of the Winchester bushel and its dependent quantities, the peck, (dry) gallon and (dry) quart. They would later become known as the Winchester Standards, named because the examples were kept in the city of Winchester.

British Empire States and dominions ruled by the United Kingdom

The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom and its predecessor states. It originated with the overseas possessions and trading posts established by England between the late 16th and early 18th centuries. At its height, it was the largest empire in history and, for over a century, was the foremost global power. By 1913, the British Empire held sway over 412 million people, 23% of the world population at the time, and by 1920, it covered 35,500,000 km2 (13,700,000 sq mi), 24% of the Earth's total land area. As a result, its political, legal, linguistic and cultural legacy is widespread. At the peak of its power, the phrase "the empire on which the sun never sets" was often used to describe the British Empire, because its expanse around the globe meant that the sun was always shining on at least one of its territories.



The Weights and Measures Act of 1824 was initially scheduled to go into effect on 1 May 1825. [3] However, the Weights and Measures Act of 1825 pushed back the date to 1 January 1826. [4] The 1824 Act allowed the continued use of pre-imperial units provided that they were customary, widely known, and clearly marked with imperial equivalents. [3]

Apothecaries' units

Imperial standards of length 1876 in Trafalgar Square, London. Imperial standards of length 1876 Trafalgar Square.jpg
Imperial standards of length 1876 in Trafalgar Square, London.

Apothecaries' units are mentioned neither in the act of 1824 nor 1825. At the time, apothecaries' weights and measures were regulated "in England, Wales, and Berwick-upon-Tweed" by the London College of Physicians, and in Ireland by the Dublin College of Physicians. In Scotland, apothecaries' units were unofficially regulated by the Edinburgh College of Physicians. The three colleges published, at infrequent intervals, pharmacopoeiae, the London and Dublin editions having the force of law. [5] [6]

Berwick-upon-Tweed town in the county of Northumberland, England

Berwick-upon-Tweed is a town in the county of Northumberland. It is the northernmost town in England, at the mouth of the River Tweed on the east coast, 2 12 miles (4 km) south of the Scottish border. Berwick is approximately 56 miles (90 km) east-south east of Edinburgh, 65 miles (105 km) north of Newcastle upon Tyne and 345 miles (555 km) north of London.

Royal College of Physicians of Ireland

The Royal College of Physicians of Ireland (RCPI), is an Irish professional body dedicated to improving the practice of general medicine and related medical specialties, chiefly through the accreditation of physicians by examination.

Pharmacopoeia Book containing directions for the identification of compound medicines

A pharmacopoeia, pharmacopeia, or pharmacopoea, in its modern technical sense, is a book containing directions for the identification of compound medicines, and published by the authority of a government or a medical or pharmaceutical society.

Imperial apothecaries' measures, based on the imperial pint of 20 fluid ounces, were introduced by the publication of the London Pharmacopoeia of 1836, [7] [8] the Edinburgh Pharmacopoeia of 1839, [9] and the Dublin Pharmacopoeia of 1850. [10] The Medical Act of 1858 transferred to The Crown the right to publish the official pharmacopoeia and to regulate apothecaries' weights and measures. [11]

The Crown is the state in all its aspects within the jurisprudence of the Commonwealth realms and their sub-divisions. Legally ill-defined, the term has different meanings depending on context. It is used to designate the monarch in either a personal capacity, as Head of the Commonwealth, or as the king or queen of his or her realms. It can also refer to the rule of law; however, in common parlance 'The Crown' refers to the functions of government and the civil service.



Metric equivalents in this article usually assume the latest official definition. Before this date, the most precise measurement of the imperial Standard Yard was 0.914398415 metres. [12]

Table of length equivalent units
UnitRelative to previousFeetMillimetres Metres Notes
thou (th)1120000.02540.0000254
Also 25.4 μm. Also known as mil [13]
inch (in) or (")1000 thou11225.40.0254
(1 metre = 39.3701 inches)
foot (ft) or (')12 inches1304.80.3048
yard (yd)3 feet3914.40.9144
Defined as exactly 0.9144 metres by the International yard and pound agreement of 1959
chain (ch)22 yards6620116.820.1168
100 links, 4 rods or 110 of a furlong. The distance between the two wickets on a cricket pitch
furlong (fur)10 chains660201.168
220 yards
mile (mi)8 furlongs52801609.344
1760 yards or 80 chains
league (lea)3 miles158404828.032
No longer an official unit in any nation.[ citation needed ]
Maritime units
fathom (ftm)2.02667 yards6.076118521.852
The British Admiralty in practice used a fathom of 6 feet. This was despite its being 11000 of a nautical mile (i.e. 6.08 feet) until the adoption of the international nautical mile. [14]
cable 100 fathoms607.61185.2
One tenth of a nautical mile. Equal to 100 fathoms under the strict definition.
nautical mile 10 cables6076.11852
Used for measuring distances at sea (and also in aviation) and approximately equal to one arc minute of a great circle. Until the adoption of the international definition of 1852 metres in 1970, the British nautical (Admiralty) mile was defined as 6080 feet. [15]
Gunter's survey units (17th century onwards)
link 7.92 inches66100201.1680.201168
1100 of a chain and 11000 of a furlong
rod 25 links6645029.25.0292
The rod is also called pole or perch and equal to 5 12 yards


UnitRelation to
units of length
Square feetSquare rodsSquare milesSquare metres Hectares Notes
perch 1 rod × 1 rod272.251110240025.292852640.002529
Although the proper term is square rod, for centuries this unit has been called a pole or perch or, more properly, square pole or square perch.
rood 1 furlong × 1 rod [16] 1089040125601011.71410560.1012
The rood is 1210 square yards.
acre 1 furlong × 1 chain4356016016404046.85642240.4047
One acre is 4840 square yards
Note: All equivalences are exact except hectares, which are accurate to 4 significant figures.


In 1824, the various different gallons in use in the British Empire were replaced by the imperial gallon, a unit close in volume to the ale gallon. It was originally defined as the volume of 10 pounds (4.5 kg) of distilled water weighed in air with brass weights with the barometer standing at 30 inches of mercury (102 kPa) at a temperature of 62  °F (17 °C). In 1963, the gallon was redefined as the volume of 10 pounds of distilled water of density 0.998859 g/mL weighed in air of density 0.001217 g/mL against weights of density 8.136 g/mL, which works out to 4.546096 l or 277.4198 cu in. The Weights and Measures Act of 1985 switched to a gallon of exactly 4.54609 L (approximately 277.4194 cu in). [17]

Inch of mercury is a unit of measurement for pressure. It is still used for barometric pressure in weather reports, refrigeration and aviation in the United States.

Fahrenheit unit of temperature

The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and salt. Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature. The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.

Table of commonly used volume units
MillilitresCubic inchesUS ouncesUS pints
fluid ounce (fl oz)1   120  28.41306251.73390.960760.060047
gill (gi)5   14  142.06531258.66944.80380.30024
pint (pt)20   1   568.2612534.67719.2151.2009
quart (qt)40   2   1136.522569.35538.4302.4019
gallon (gal)160   8   4546.09277.42153.729.6076
Note: The millilitre equivalences are exact, but cubic-inch and US measures are correct to 5 significant figures.
Legal measures from 1826–1870 [18]
LiquidDryCapacity (in³)
1/2 gill4.3
Gill1/4 pint8.7
1/2 pint1/2 pint17.4
1/2 gallon1/4 peck or 1/2 gallon138.7
Gallon1/2 peck or gallon277.4
2 gallons (peck)Peck554.8
4 gallons (1/2 bushel)1/2 bushel1109.7

British apothecaries' volume measures

These measurements were in use from 1826, when the new imperial gallon was defined, but were officially abolished in the United Kingdom on 1 January 1971. [19] [20] In the US, though no longer recommended, the apothecaries' system is still used occasionally in medicine, especially in prescriptions for older medications. [21] [22]

Table of British apothecaries' volume units [nb 1]
UnitSymbols &
Relative to
metric value [note 1]
minim ♏︎, Mx, a symbol for minim in the apothecaries' system.svg , m, m., min 59.1938802083  µL
fluid scruple fl ℈, fl s20 minims1.18387760416 mL
fluid drachm
(fluid dram, fluidram)
ʒ, fl ʒ, fʒ, ƒ 3, fl dr3 fluid scruples3.5516328125 mL
fluid ounce ℥, fl ℥, f℥, ƒ ℥, fl oz8 fluid drachms28.4130625 mL
pint O, pt20 fluid ounces568.26125 mL
gallon C, gal8 pints4.54609 L
  1. The vinculum over numbers (e.g. 3) represents a repeating decimal.

Mass and weight

In the 19th and 20th centuries, the UK used three different systems for mass and weight.

The distinction between mass and weight is not always clearly drawn. Strictly a pound is a unit of mass, although it is commonly referred to as a weight. When a distinction is necessary, the term pound-force may be used to refer to a unit of force rather than mass. The troy pound (373.2417216 g) was made the primary unit of mass by the 1824 Act; however, its use was abolished in the UK on 1 January 1879, [29] with only the troy ounce (31.1034768 g) and its decimal subdivisions retained. [30] The Weights and Measures Act 1855 (18 & 19 Victoria C72) made the avoirdupois pound the primary unit of mass. [31] In all the systems, the fundamental unit is the pound, and all other units are defined as fractions or multiples of it.

Table of mass units
grain (gr)170000.06479891Exactly 64.79891 milligrams.
drachm (dr)12561.7718451953125
ounce (oz)11628.349523125
pound (lb)1453.592370.45359237Defined by The Units of Measurement Regulations 1994 Act (amended 2000) [32]
stone (st)146350.293186.35029318The plural stone is often used when providing a weight (e.g. "this sack weighs 8 stone"). [33] A person's weight is often quoted in stones and pounds in English-speaking countries that use the avoirdupois system, with the exception of the United States and Canada, where it is usually quoted in pounds.
quarter (qr or qtr)2812.70058636 One quarter is equal to two stones or a quarter of a hundredweight. The term quarter was also commonly used to refer to a quarter of a pound in a retail context.
hundredweight (cwt)11250.80234544One imperial hundredweight is equal to eight stones. This is the long hundredweight as opposed to the short hundredweight of 100 pounds as used in the United States and Canada. [34]
ton (t)22401016.0469088Twenty hundredweights equal a ton (as with the US and Canadian [34] systems). The imperial hundredweight is 12% greater than the US and Canadian equivalent. The imperial ton (or long ton) is 2240 pounds, which is much closer to a metric tonne (about 2204.6 pounds), compared to the short ton of 2000 pounds (907.185 kg).
Gravitational units
slug (slug)32.1740485614593.9029414.59390294The slug, a unit associated with imperial and US customary systems, is a mass that accelerates by 1 ft/s2 when a force of one pound (lbf) is exerted on it. [35]
F = ma (Newton's second law)
1 lbf = 1 slug × 1 ft/s2 (as defined above)
1 lbf = 1 lb × g/gc (by definition of the pound force[ citation needed ])
g 32.17404856 ft/s2gc 32.17404856 lbm.ft/lbf.s2
1 slug 32.17404856 pounds

Natural equivalents

Although the 1824 act defined the yard and pound by reference to the prototype standards, it also defined the values of certain physical constants, to make provision for re-creation of the standards if they were to be damaged. For the yard, the length of a pendulum beating seconds at the latitude of Greenwich at Mean Sea Level in vacuo was defined as 39.01393 inches. For the pound, the mass of a cubic inch of distilled water at an atmospheric pressure of 30 inches of mercury and a temperature of 62° Fahrenheit was defined as 252.458 grains, with there being 7,000 grains per pound. [3] However, following the destruction of the original prototypes in the 1834 Houses of Parliament fire, it proved impossible to recreate the standards from these definitions, and a new Weights and Measures Act (18 & 19 Victoria. Cap. 72) was passed in 1855 which permitted the recreation of the prototypes from recognized secondary standards. [31]

Relation to other systems

English units of length English Length Units Graph.svg
English units of length

The imperial system is one of many systems of English units. Although most of the units are defined in more than one system, some subsidiary units were used to a much greater extent, or for different purposes, in one area rather than the other. The distinctions between these systems are often not drawn precisely.

One such distinction is that between these systems and older British/English units/systems or newer additions. The term imperial should not be applied to English units that were outlawed in the Weights and Measures Act 1824 or earlier, or which had fallen out of use by that time, nor to post-imperial inventions, such as the slug or poundal.

The US customary system is historically derived from the English units that were in use at the time of settlement. Because the United States was already independent at the time, these units were unaffected by the introduction of the imperial system.

Current use

A baby bottle that measures in three measurement systems--metric, imperial (UK), and US customary. MetricImperialUSCustomaryUnits.jpg
A baby bottle that measures in three measurement systems—metric, imperial (UK), and US customary.

United Kingdom

British law now defines each imperial unit in terms of the metric equivalent. The metric system is in official use within the United Kingdom for most official applications with Imperial units remaining in widespread use amongst the public. [36] All UK roads use the imperial system except for weight limits, and newer height or width restriction signs give metric alongside imperial. [37]

Units of measurement regulations require all measuring devices used in trade or retail to display measurements in metric quantities. Almost all traders in the UK will accept requests from customers specified in imperial units, and scales which display in both unit systems are commonplace in the retail trade. Metric price signs may be accompanied by imperial price signs provided that the imperial signs are no larger and no more prominent than the metric ones.

The United Kingdom completed its official partial transition to the metric system in 1995, with some imperial units still legally mandated for certain applications such as draught beer and cider, [38] road-signs, [39] and therefore the speedometers on vehicles sold in the UK must be capable of displaying miles per hour. Even though the troy pound was outlawed in the UK in the Weights and Measures Act of 1878, the troy ouncemay still be used for the weights of precious stones and metals. The original railways (many built in the Victorian era) are a big user of imperial units, with distances officially measured in miles and yards or miles and chains, and also feet and inches, and speeds are in miles per hour, although more recent systems are metric, and London Underground uses metric. [40]

Most British people still use imperial units in everyday life for distance (miles, yards, feet and inches) and volume in some cases (especially milk and beer in pints) but rarely for canned or bottled soft drinks or petrol. [36] [41] Though use of kilograms is increasing, most British people also still use imperial units in everyday life for body weight (stones and pounds for adults, pounds and ounces for babies).[ citation needed ] Some government documents aimed at the public give body weight and height not only in metric units (kilograms centimetres) but also in imperial units (stones and pounds, feet and inches). [42] A survey in 2015 found that many people did not know their body weight or height in one system or the other. [43] People under the age of 40 preferred the metric system but people aged 40 and over preferred the imperial system. [44] The height of horses in some English-speaking countries, including Australia, [1] Canada, the United Kingdom and the United States is usually measured in hands, standardized to 4 inches (101.6 mm). Fuel consumption for vehicles is commonly stated in miles per gallon, though official figures always include litres per 100 km equivalents. When sold draught in licensed premises, beer and cider must be sold in pints and half-pints. Cow's milk is available in both litre- and pint-based containers in supermarkets and shops. Areas of land associated with farming, forestry and real estate are commonly advertised in acres and square feet, but for official government purposes the units are always hectares and square metres.

Office space and industrial units are usually advertised in square feet. Steel pipe sizes are sold in increments of inches, while copper pipe is sold in increments of millimetres. Road bicycles have their frames measured in centimetres, while off-road bicycles have their frames measured in inches. The size (diagonal) of television and computer monitor screens is always denominated in inches. Food sold by length or width e.g. pizzas or sandwiches, is generally sold in inches. Clothing is always sized in inches, with the metric equivalent often shown as a small supplementary indicator. Gas is usually measured by the cubic foot or cubic metre, but is billed like electricity by the kilowatt hour. [45]

Some pre-packaged products show both metric and imperial measures and it is also common to see imperial pack sizes with metric only labels e.g. a 1 lb (i.e., 454 g) tin of Lyle's Golden Syrup is always labelled 454 g with no imperial indicator. Similarly most jars of jam and packs of sausages are labelled 454 g with no imperial indicator.


India's conversion to the metric system from the imperial system occurred in stages between 1955 and 1962. The metric system in weights and measures was adopted by the Indian Parliament in December 1956 with the Standards of Weights and Measures Act, which took effect beginning 1 October 1958. The Indian Coinage Act was passed in 1955 by the Government of India to introduce decimal coinage in the country. The new system of coins became legal tender on April 1957, where the rupee consists of 100 paise. For the next five years, both the previous and new systems were legal. In April 1962, all other systems were banned. This process of metrication is called "big-bang" route, which is to simultaneously outlaw the use of pre-metric measurement, metricise, reissue all government publications and laws, and change education systems to metric. [46]

Today all official measurements are made in the metric system. However, in common usage some older Indians may still refer to imperial units. Some measurements, such as the heights of mountains, are still recorded in feet. Additionally, the Indian numbering system of crores and lacs is used alongside otherwise metricated currency units, while tyre rim diameters are still measured in inches, as used worldwide. Road widths are popularly measured in feet but official documents use metres. Body temperature is still sometimes measured in degrees Fahrenheit. Industries like the construction and the real estate industry still use both the metric and the imperial system though it is more common for sizes of homes to be given in square feet and land in acres. Bulk cotton is sold by the candy (0.35 imperial tons, or 355.62 kg) or the bale (170 kg). [46] [47]

In Standard Indian English, as in Australian, Singaporean, and British English, metric units such as the litre (liter), metre (meter), and metric tonne (ton) utilise the traditional spellings brought over from French, which differ from those used in the United States and the Philippines. The imperial long ton is invariably spelt with one 'n'. (See English in the Commonwealth of Nations for more information). [47]

Hong Kong

Hong Kong has three main systems of units of measurement in current use:

In 1976 the Hong Kong Government started the conversion to the metric system, and as of 2012 measurements for government purposes, such as road signs, are almost always in metric units. However, all three systems are officially permitted for trade, [48] and in the wider society a mixture of all three systems prevails.

The Chinese system's most commonly used units for length are (li), (tseung/cheung), (tsek/chek), (tsun/chun), (fen/fan) in descending scale order. These units are now rarely used in daily life, the imperial and metric systems being preferred. The imperial equivalents are written with the same basic Chinese characters as the Chinese system. In order to distinguish between the units of the two systems, the units can be prefixed with "Ying" (Chinese :) for the Imperial system and "Wa" (Chinese :) for the Chinese system. In writing, derived characters are often used, with an additional (mouth) radical to the left of the original Chinese character, for writing imperial units. The most commonly used units are the mile or "li" (Chinese :), the yard or "ma" (Chinese :), the foot or "chek" (Chinese :), and the inch or "tsun" (Chinese :).

The traditional measure of flat area is the square foot (Chinese :方呎, 平方呎) of the imperial system, which is still in common use for real estate purposes. The measurement of agricultural plots and fields, however, is traditionally conducted in (mau) of the Chinese system.

For the measurement of volume, Hong Kong officially uses the metric system, though the gallon (加侖, ka-lun) is also occasionally used.


A one US gallon gas can purchased near the US-Canada border. It shows equivalences in imperial gallons and litres. GasCan.jpg
A one US gallon gas can purchased near the US-Canada border. It shows equivalences in imperial gallons and litres.

During the 1970s, the metric system and SI units were introduced in Canada to replace the imperial system. Within the government, efforts to implement the metric system were extensive; almost any agency, institution, or function provided by the government uses SI units exclusively. Imperial units were eliminated from all road signs, although both systems of measurement will still be found on privately owned signs, such as the height warnings at the entrance of a parkade. In the 1980s, momentum to fully convert to the metric system stalled when the government of Brian Mulroney was elected. There was heavy opposition to metrication and as a compromise the government maintains legal definitions for and allows use of imperial units as long as metric units are shown as well. [49] [50] [51] The law requires that measured products (such as fuel and meat) be priced in metric units, although an imperial price can be shown if a metric price is present. [52] [53] However, there tends to be leniency in regards to fruits and vegetables being priced in imperial units only. Environment Canada still offers an imperial unit option beside metric units, even though weather is typically measured and reported in metric units in the Canadian media. However, some radio stations near the United States border (such as CIMX and CIDR) primarily use imperial units to report the weather. Railways in Canada also continue to use Imperial units.

Imperial units are still used in ordinary conversation. Today, Canadians typically use a mix of metric and imperial measurements in their daily lives. However, the use of the metric and imperial systems varies by age. The older generation mostly uses the imperial system, while the younger generation more often uses the metric system. Newborns are measured in SI at hospitals, but the birth weight and length is also announced to family and friends in imperial units. Drivers' licences use SI units. In livestock auction markets, cattle are sold in dollars per hundredweight (short), whereas hogs are sold in dollars per hundred kilograms. Imperial units still dominate in recipes, construction, house renovation and gardening. [54] [55] [56] [57] [58] Land is now surveyed and registered in metric units, although initial surveys used imperial units. For example, partitioning of farm land on the prairies in the late 19th and early 20th centuries was done in imperial units; this accounts for imperial units of distance and area retaining wide use in the Prairie Provinces. The size of most apartments, condominiums and houses continues to be described in square feet rather than square metres, and carpet or flooring tile is purchased by the square foot. Motor-vehicle fuel consumption is reported in both litres per 100 km and statute miles per imperial gallon, [59] leading to the erroneous impression that Canadian vehicles are 20% more fuel-efficient than their apparently identical American counterparts for which fuel economy is reported in statute miles per US gallon (neither country specifies which gallon is used). Canadian railways maintain exclusive use of imperial measurements to describe train length (feet), train height (feet), capacity (tons), speed (mph), and trackage (miles). [60]

Imperial units also retain common use in firearms and ammunition. Imperial measures are still used in the description of cartridge types, even when the cartridge is of relatively recent invention (e.g., .204 Ruger, .17 HMR, where the calibre is expressed in decimal fractions of an inch). However, ammunition that is already classified in metric is still kept metric (e.g., 9×19mm). In the manufacture of ammunition, bullet and powder weights are expressed in terms of grains for both metric and imperial cartridges.

As in most of the western world, air navigation is based on nautical units, e.g., the nautical mile, which is neither imperial nor metric, though altitude is still measured in imperial feet [61] in keeping with the international standard.


Metrication in Australia has largely ended the official use of imperial units, though for particular measurements (such as flight altitudes[ citation needed ] and nominal sizes of computer and television screens) international use of imperial units is still followed. In licensed venues, draught beer and cider is sold in glasses and jugs with sizes based on the imperial fluid ounce though rounded to the nearest 5 mL.

New Zealand

Although New Zealand completed metrication in the 1970s, a study of university students undertaken in 1992 found a continued use of imperial units for birth weight and human height alongside metric units. [62]

In aviation, altitude and airport elevation are measured in feet whilst navigation is done in nautical miles; all other aspects (fuel quantity, aircraft weight, runway length, etc.) use metric units.

Screen sizes for devices such as televisions, [63] monitors [64] and phones, [65] and wheel rim sizes for vehicles, [66] are stated in inches, as is the convention in the rest of the world.


Ireland has officially changed over to the metric system since entering the European Union, with distances on new road signs being metric since 1997 and speed limits being metric since 2005. The imperial system remains in limited use – for sales of beer in pubs (traditionally sold by the pint). All other goods are required by law to be sold in metric units, although old quantities are retained for some goods like butter and sausages, which are sold in 454-gram (1 lb) packaging. The majority of cars sold pre-2005 feature speedometers with miles per hour as the primary unit, but with a kilometres per hour display as well.

Other countries

Full imperial measurements are used in Palau, Marshall Islands, Micronesia and Belize. Some imperial measurements remain in limited use in Malaysia, the Philippines, Sri Lanka and South Africa. Measurements in feet and inches, especially for a person's height, are frequently encountered in conversation and non-governmental publications.

Prior to metrication, it was a common practice in Malaysia for people to refer to unnamed locations and small settlements along major roads by referring to how many miles the said locations were located from the nearest major town. In some cases, these eventually became the official names of the locations; in other cases, such names have been largely or completely superseded by new names. An example of the former is Batu 32 (literally "Mile 32" in Malay), which refers to the area surrounding the intersection between Federal Route 22 (the Tamparuli-Sandakan highway) and Federal Route 13 (the Sandakan-Tawau highway). The area is so named because it is 32 miles west of Sandakan, the nearest major town.

Petrol is still sold by the imperial gallon in Anguilla, Antigua and Barbuda, Belize, Myanmar, the Cayman Islands, Dominica, Grenada, Montserrat, St Kitts and Nevis and St. Vincent and the Grenadines. The United Arab Emirates Cabinet in 2009 issued the Decree No. (270 / 3) specifying that, from 1 January 2010, the new unit sale price for petrol will be the litre and not the gallon. This in line with the UAE Cabinet Decision No. 31 of 2006 on the national system of measurement, which mandates the use of International System of units as a basis for the legal units of measurement in the country. [67] [68] Sierra Leone switched to selling fuel by the litre in May 2011. [69]

In October 2011, the Antigua and Barbuda government announced the re-launch of the Metrication Programme in accordance with the Metrology Act 2007, which established the International System of Units as the legal system of units. The Antigua and Barbuda government has committed to a full conversion from the imperial system by the first quarter of 2015. [70]

See also


  1. References for the Table of British apothecaries' volume units: Unit column; [23] [24] :C-7 [25] Symbols & abbreviations column; [21] [22] [23] [24] :C-5, C-17–C-18 [25] [26] [27] Relative to previous column; [23] [24] :C-7Exact metric value column — fluid ounce, pint and gallon, [28] all other values calculated using value for fluid ounce and the Relative to previous column's values.

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In recipes, quantities of ingredients may be specified by mass, by volume, or by count.

Pint imperial and customary unit of measurement

The pint is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one-eighth of a gallon. The British imperial pint is about 20% larger than the American pint because the two systems are defined differently. Almost all other countries have standardized on the metric system, so the size of what may be called a pint varies depending on local custom.

The minim is a unit of volume in both the imperial and US customary systems of measurement. Specifically it is ​160 of a fluidram or ​1480 of a fluid ounce. In the Pharmacopoeia, it is also noted that the minim was originally created by Mr Timothy Lane, F.R.S., as 61440 parts per wine gallon.

Long ton, also known as the imperial ton or displacement ton, is the name for the unit called the "ton" in the avoirdupois system of weights or Imperial system of measurements. It was standardised in the thirteenth century and is used in the United Kingdom and several other British Commonwealth of Nations countries alongside the mass-based metric tonne defined in 1799.

Metrication in the United States

Metrication is the process of introducing the International System of Units, also known as SI units or the metric system, to replace a jurisdiction's traditional measuring units. Although U.S. customary units have been defined in terms of metric units since the 19th century, as of 2019 the United States is one of only three countries that have not officially adopted the metric system as the primary means of weights and measures.

The dram is a unit of mass in the avoirdupois system, and both a unit of mass and a unit of volume in the apothecaries' system. It was originally both a coin and a weight in ancient Greece. The unit of volume is more correctly called a fluid dram, fluid drachm, fluidram or fluidrachm.

Apothecaries system historical system of mass and volume units that were used by physicians and apothecaries for medical recipes

The apothecaries' system or apothecaries' weights and measures is a historical system of mass and volume units that were used by physicians and apothecaries for medical recipes, and also sometimes by scientists. The English version of the system is closely related to the English troy system of weights, the pound and grain being exactly the same in both. It divides a pound into 12 ounces, an ounce into 8 drachms, and a drachm into 3 scruples or 60 grains. This exact form of the system was used in the United Kingdom; in some of its former colonies it survived well into the 20th century. The apothecaries' system of measures is a similar system of volume units based on the fluid ounce. For a long time, medical recipes were written in Latin, often using special symbols to denote weights and measures.

A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Systems of measurement in use include the International System of Units (SI), the modern form of the metric system, the imperial system, and United States customary units.

English units are the units of measurement that were used in England up to 1826, which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.

The spread of metrication around the world in the last two centuries has been met with both support and opposition. All countries except Burma (Myanmar), Liberia, and the United States of America have officially adopted the metric system, although Liberia has seen some introduction of metric units, and in 2013 Burma formally announced the beginning of its metrication program. The metric system has been largely adopted in the United Kingdom, Canada and Ireland, without having fully displaced the imperial units from all areas of life. In other Anglophone countries such as Australia, Singapore and New Zealand, imperial units have been formally deprecated and are no longer officially sanctioned for use.

Metrication in Canada

Metrication in Canada began in 1970 and while Canada has converted to the metric system for many purposes, there is still significant use of non-metric units and standards in many sectors of the Canadian economy. This is mainly due to historical ties with the United Kingdom, the traditional use of the imperial system of measurement in Canada, proximity to the United States, and to public opposition to metrication during the transition period.

Metrication in the United Kingdom Chronology of metrication and metrication-related events in the United Kingdom

Metrication in the United Kingdom, the process of introducing the metric system of measurement in place of imperial units, has made steady progress since the mid–20th century but today remains equivocal and varies by context. Most of government, industry and commerce use metric units, but imperial units are officially used to specify journey distances, vehicle speeds and the sizes of returnable milk containers, beer and cider glasses. Imperial units are also often used to describe body measurements and vehicle fuel economy. In schools metric units are taught and used as the norm and imperial units that remain in common usage in the UK must also be taught.

Metrication or metrification is the process of converting to the metric system based on the International System of Units (SI). India's conversion to the metric system occurred in stages between 1955 and 1962. The metric system in weights and measures was adopted by the Indian Parliament in December 1956 with the Standards of Weights and Measures Act, which took effect beginning 1 October 1958. The Indian Coinage Act was passed in 1955 by the Government of India to introduce decimal coinage in the country. The new system of coins became legal tender on April 1957, where the rupee consists of 100 paise. For the next five years, both the old and new systems were legal. In April 1962, all other systems were banned. This process of metrication is called "big-bang" route, which is to simultaneously outlaw the use of pre-metric measurement, metricise, reissue all government publications and laws, and change education systems to metric.

Metrication in Ireland

Ireland gradually adopted the British imperial measurement system, fully replacing traditional Irish measure during the 19th century, and these units continued to be used after Irish independence. In 1980 the European Union asked all of its member states to convert to the metric system, and in Ireland and the UK this process was originally to have been completed by 2009. Metrication progressed in Ireland with, for example, the changeover to metric on road signs and speed limits being completed by 2005. By 2007 the changeover was far from complete, so the EU abandoned its policy to make the metric system compulsory for Ireland and the UK, allowing for both the metric and imperial systems to remain in use indefinitely. The metrication process is still ongoing in Ireland, with both measurements widely used.

Comparison of the imperial and US customary measurement systems

Both the imperial and United States customary systems of measurement derive from earlier English systems used in the Middle Ages, that were the result of a combination of the local Anglo-Saxon units inherited from German tribes and Roman units brought by William the Conqueror after the Norman Conquest of England in 1066.

The Weights and Measures Act is a Canadian law governing the units of measurements used in Canada.

Hong Kong units of measurement

Hong Kong has three main systems of units of measurement in current use:

Imperial and US customary measurement systems English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure

The imperial system of measurement and the US customary system of measurement are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.


  1. Britannica Educational Publishing (1 August 2010). The Britannica Guide to Numbers and Measurement. The Rosen Publishing Group. p. 241. ISBN   978-1-61530-218-5 . Retrieved 10 December 2011.
  2. Chaney, Henry James (1897). A Practical Treatise on the Standard Weights and Measures in Use in the British Empire with some account of the metric system. Eyre and Spottiswoode. p. 3. Retrieved 11 September 2016.
  3. 1 2 3 Great Britain (1824). The statutes of the United Kingdom of Great Britain and Ireland (1807-1865). His Majesty's statute and law printers. pp. 339–354. Retrieved 31 December 2011.
  4. Great Britain; William David Evans; Anthony Hammond; Thomas Colpitts Granger (1836). A collection of statutes connected with the general administration of the law: arranged according to the order of subjects. W. H. Bond. pp. 306–27. Retrieved 31 December 2011.
  5. Edinburgh medical and surgical journal. A. and C. Black. 1824. p. 398. Retrieved 29 July 2012.
  6. Ireland; Butler, James Goddard; Ball, William (barrister.) (1765). The Statutes at Large, Passed in the Parliaments Held in Ireland: From the twenty-third year of George the Second, A.D. 1749, to the first year of George the Third, A.D. 1761 inclusive. Boulter Grierson. p. 852. Retrieved 29 July 2012.
  7. Gray, Samuel Frederick (1836). A supplement to the Pharmacopœia and treatise on pharmacology in general: including not only the drugs and preparations used by practitioners of medicine, but also most of those employed in the chemical arts : together with a collection of the most useful medical formulæ ... Longman, Rees, Orme, Brown, Green, and Longman. p. 516. Retrieved 29 July 2012.
  8. "A Translation of the Pharmacopoeia of the Royal College of Physicians of London, 1836.: With ..."
  9. The Pharmacopoeia of the Royal College of Physicians of Edinburgh. Adam and Charles Black and Bell and Bradfute. 1839. pp. xiii–xiv. Retrieved 29 July 2012.
  10. Royal College of Physicians of Dublin; Royal College of Physicians of Ireland (1850). The pharmacopœia of the King and queen's college of physicians in Ireland. Hodges and Smith. p. xxii. Retrieved 29 July 2012.
  11. Great Britain (1858). A collection of the public general statutes passed in the ... year of the reign of ... Printed by G. W. Eyre and W. Spottiswoode, Printers to the Queen. p. 306. Retrieved 29 July 2012.
  12. Sears et al. 1928. Phil Trans A, 227:281.
  13. Mil at How Many? A Dictionary of Units of Measurement by Russ Rowlett
  14. The exact figure was 6.08 feet, but 6 feet was in use in practice. The commonly accepted definition of a fathom was always 6 feet. The conflict was inconsequential, as Admiralty nautical charts designated depths shallower than 5 fathoms in feet on older imperial charts. Today, all charts worldwide are metric, except for USA Hydrographic Office charts, which use feet for all depth ranges.
  15. The nautical mile was not readily expressible in terms of any of the intermediate units, because it was derived from the circumference of the Earth (like the original metre).
  16. "Appendix C: General Tables of Units of Measurements" (PDF). NIST. Archived from the original (PDF) on 26 November 2006. Retrieved 4 January 2007.
  17. "imperial gallon".
  18. Ricketts, Carl (1996). Marks and Marking of Weights and Measures of the British Isles. Taunton, Somerset: Devon Design and Print. p. 94. ISBN   0952853302 . Retrieved 13 September 2016.
  19. "The Weights and Measures (Equivalents for dealings with drugs) Regulations 1970".
  20. "Museum of the Royal Pharmaceutical Society, London, Information Sheet: 11" (PDF).
  21. 1 2 Zentz, Lorraine C. (2010). "Chapter 1: Fundamentals of Math — Apothecary System". Math for Pharmacy Technicians. Sudbury, MA: Jones & Bartlett Learning. pp. 7–8. ISBN   978-0-7637-5961-2. OCLC   421360709 . Retrieved 6 July 2012.
  22. 1 2 Boyer, Mary Jo (2009). "UNIT 2 Measurement Systems: The Apothecary System". Math for Nurses: A Pocket Guide to Dosage Calculation and Drug Preparation (7th ed.). Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams & Wilkins. pp. 108–9. ISBN   978-0-7817-6335-6. OCLC   181600928 . Retrieved 6 July 2012.
  23. 1 2 3 Royal College of Physicians of Dublin (1850). "Weights and Measures". The Pharmacopœia of the King and Queen's College of Physicians in Ireland. Dublin: Hodges and Smith. p. xlvi. OCLC   599509441 . Retrieved 6 July 2012.
  24. 1 2 3 National Institute of Standards and Technology (October 2011). Butcher, Tina; Cook, Steve; Crown, Linda et al. eds. "Appendix C – General Tables of Units of Measurement" (PDF). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. NIST Handbook. 44 (2012 ed.). Washington, D.C.: US Department of Commerce, Technology Administration, National Institute of Standards and Technology. ISSN 0271-4027. OCLC OCLC   58927093. Retrieved 6 July 2012.
  25. 1 2 Rowlett, Russ (13 September 2001). "F". How Many? A Dictionary of Units of Measurement. Chapel Hill, NC: University of North Carolina at Chapel Hill. fluid dram or fluidram (fl dr). Retrieved 6 July 2012.
  26. Buchholz, Susan; Henke, Grace (2009). "Chapter 3: Metric, Apothecary, and Household Systems of Measurement — Table 3-1: Apothecary Abbreviations". Henke's Med-Math: Dosage Calculation, Preparation and Administration (6th ed.). Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams & Wilkins. p. 55. ISBN   978-0-7817-7628-8. OCLC   181600929 . Retrieved 6 July 2012.
  27. Pickar, Gloria D.; Swart, Beth; Graham, Hope; Swedish, Margaret (2012). "Appendix B: Apothecary System of Measurement — Apothecary Units of Measurement and Equivalents". Dosage Calculations (2nd Canadian ed.). Toronto: Nelson Education. p. 528. ISBN   978-0-17-650259-1. OCLC   693657704 . Retrieved 6 July 2012.
  28. United Kingdom; Department of Trade and Industry (1995). The Units of Measurement Regulations 1995. London: HMSO. Schedule: Relevant Imperial Units, Corresponding Metric Units and Metric Equivalents. ISBN   978-0-11-053334-6. OCLC   33237616 . Retrieved 1 July 2012.
  29. Great Britain (1878). Statutes at large ... p. 308. Retrieved 12 September 2012.
  30. Chisholm, Hugh (1911). The Encyclopædia Britannica: A Dictionary of Arts, Sciences, Literature and General Information. At the University Press. p. 480. Retrieved 12 September 2012.
  31. 1 2 Great Britain (1855). A collection of public general statutes passed in the 18th and 19th years of the reign of Her Majesty Queen Victoria. pp. 273–75. Retrieved 5 January 2012.
  32. "The Units of Measurement Regulations 1994". Retrieved 13 March 2019.
  33. "Definition of stone in English from the Oxford dictionary". Oxford University Press. Retrieved 25 November 2015.
  34. 1 2 Weights and Measures Act Archived 16 October 2012 at the Wayback Machine
  35. "Wolfram-Alpha: Computational Knowledge Engine".
  36. 1 2 Kelly, Jon (21 December 2011). "Will British people ever think in metric?". BBC. Retrieved 26 February 2017. ...but today the British remain unique in Europe by holding onto imperial weights and measures. ...the persistent British preference for imperial over metric is particularly noteworthy...
  37. "Height and width road signs to display metric and imperial". BBC. 8 November 2014. Retrieved 26 February 2017. New road signs showing height and width restrictions will use both metric and imperial measurements from March 2015....Road signs for bridges, tunnels and narrow roads can currently show measurements in just feet and inches or only metres. Some already display both.
  38. "BusinessLink: Weights and measures: Rules for pubs, restaurants and cafes". Department for Business, Innovation & Skills. Archived from the original (online) on 20 July 2011. Retrieved 24 August 2009.
  39. "Department for Transport statement on metric road signs" (online). BWMA. 12 July 2002. Retrieved 24 August 2009.
  40. "Facts & Figures". Transport for London. Transport for London. Retrieved 31 January 2016.
  41. "In praise of ... metric measurements". The Guardian. London. 1 December 2006. Retrieved 29 October 2017.
  42. "BMI healthy weight calculator". National Health Service . Retrieved 25 November 2015.
  43. Dahlgreen, Will (20 June 2015). "Britain's metric muddle not changing any time soon" . Retrieved 29 October 2017. even today [2015] most 18-24 year-olds still do not know how much they weigh in kilograms (60%) or how tall they are in metres and centimetres (54%).
  44. "YouGov Survey Results" (PDF). 2015. Retrieved 29 October 2017.
  45. Government website
  46. 1 2 "internat.htm". Archived from the original on 21 February 1999.
  47. 1 2 Acharya, Anil Kumar. History of Decimalisation Movement in India, Auto-Print & Publicity House, 1958.
  49. "Weights and Measures Act: Canadian units of measure". Justice Canada. Archived from the original on 5 June 2011. Retrieved 14 November 2007.
  50. "Guide to Food Labelling and Advertising". Canadian Food Inspection Agency. Archived from the original on 24 January 2008. Retrieved 1 December 2007.|chapter= ignored (help)
  51. "Consumer Packaging and Labelling Regulations (C.R.C., c. 417)". Justice Canada, Legislative Services Branch. Retrieved 15 November 2012.
  52. "A Canadian compromise". CBC. Retrieved 11 March 2008.
  53. "Les livres et les pieds, toujours présents (eng:The pounds and feet, always present)" (in French). 5 sur 5, Société Radio-Canada . Retrieved 11 March 2008.
  55. [ dead link ]
  56. [ dead link ]
  57. [ dead link ]
  58. "Home Hardware - Building Supplies - Building Materials - Fence Products". Archived from the original on 29 June 2011. Retrieved 5 March 2011.
  59. Canada, Government of Canada, Natural Resources. "Fuel Consumption Ratings Search Tool - Conventional Vehicles".
  60. Canada, Government of Canada, Transportation Safety Board of. "Railway Investigation Report R96W0171".
  61. "Canadian Aviation Regulations, Langley Flying School. Canadian Airport Organization, Runways and Taxiways, Mandatory Instruction Signs, Manoeuvring Area, Windsocks, Airport Circuit Organization in Canada, Uncontrolled Airports, Rules for Joining the Circuit in Canada, Airports with Mandatory Radio Frequency, Controlled Airports in Canada, ATC clearances and instructions, Canadian Airspace Organization, Canadian Class C Airspace, Canadian Class D Airspace, Restricted Airspace in Canada, Airway organization in Canada, VHF Airways, Control Zones in Canada, VFR Weather Minimum in Canada, Special VFR Clearances in Canada, VFR Over-the-top, Aircraft cruising altitude rules in Canada, Altimeter Rules in Canada, VFR Flight Plans in Canada, NOTAMs in Canada, National Security rules for aircraft in Canada, Emergency Locator Transmitters, Priority Aircraft Radio Communications in Canada, Transponder Requirements in Canada, Aircraft Fuel Requirements in Canada, Aircraft Passenger Briefings in Canada, Pilot Privileges in Canada, Aircraft Wake Turbulence, Aircraft Jet Blast Hazard, Aircraft passenger seat requirements in Canada, Aircraft Oxygen requirements in Canada, Aircraft Documents required in Canada, Aircraft Equipment requirements in Canada, Aircraft Icing, Minimum flight altitude in Canada, Rules of the Air in Canada,".
  62. "Human use of metric measures of length" Archived 9 February 2013 at the Wayback Machine . Dignan, J. R. E., & O'Shea, R. P. (1995). New Zealand Journal of Psychology, 24, 21–25.
  63. "TV buying guide". Noel Leeming. Retrieved 17 September 2018.
  64. "Shop for Monitor, Computer Monitors, Computer Monitor". Harvey Norman. Retrieved 17 September 2018.
  65. "Mobile Phones, Smartphones | Spark NZ". Retrieved 17 September 2018.
  66. "Tyre Sizes | How To Read Your Tyre Size | Dimensions Explained". Retrieved 17 September 2018.
  67. "The Government of Grenada – The Ministry of Agriculture". Archived from the original on 24 March 2008. Retrieved 15 January 2008. he price of gasoline at the pumps was fixed at EC$7.50 per imperial gallon..., "Belize Ministry of Finance::FAQ". Belize Ministry of Finance. Retrieved 15 January 2008. #Kerosene per US Gallon (per Imperial gallon)#Gasoline (Regular)(per imperial Gallon)# Gasoline (Premium) (per Imperial Gallon)#Diesel (per Imperial Gallon)[ permanent dead link ]
  68. "The High Commission Antigua and Barbuda". Archived from the original on 31 January 2009. Retrieved 15 January 2008., "FuelPrices2005" (PDF). German Technical Cooperation. p. 96. Retrieved 15 January 2008.[ permanent dead link ]
  69. Sierra Leone Embassy to the United States INTRODUCTION OF THE METRIC SYSTEM AND THE PRICE OF PETROLEUM PRODUCTS Archived 29 April 2015 at the Wayback Machine Retrieved 23 October 2011.
  70. "Minister Lovell Addresses Metric Conversions". CARIBARENA Antigua. 18 October 2011. Archived from the original on 20 October 2011. Retrieved 23 October 2011.