The former Weights and Measures office in Seven Sisters, London (590 Seven Sisters Road)
The imperial system of units, imperial system or imperial units (also known as British Imperial[1] or Exchequer Standards of 1826) is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.
By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, but imperial units are still used alongside metric units in the United Kingdom and in some other parts of the former empire, notably Canada.
The Weights and Measures Act 1824 was initially scheduled to go into effect on 1 May 1825.[4] The Weights and Measures Act 1825 pushed back the date to 1 January 1826.[5] The 1824 Act allowed the continued use of pre-imperial units provided that they were customary, widely known, and clearly marked with imperial equivalents.[4]
Imperial apothecaries' measures, based on the imperial pint of 20 fluid ounces, were introduced by the publication of the London Pharmacopoeia of 1836,[8][9] the Edinburgh Pharmacopoeia of 1839,[10] and the Dublin Pharmacopoeia of 1850.[11] The Medical Act 1858 transferred to The Crown the right to publish the official pharmacopoeia and to regulate apothecaries' weights and measures.[12]
Units
Length
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.[13]
The British Admiralty in practice used a fathom of 6ft. This was despite its being 1⁄1000 of a nautical mile (i.e. 6.08ft) until the adoption of the international nautical mile.[15]
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 1852m in 1970, the British nautical (Admiralty) mile was defined as 6080ft.[16]
Note: *The square rod has been called a pole or perch or, more properly, square pole or square perch for centuries.
Volume
Imperial volume units, illustrated as jugs of various sizes.
The Weights and Measures Act 1824 invalidated the various different gallons in use in the British Empire, declaring them to be replaced by the statute gallon (which became known as the imperial gallon), a unit close in volume to the ale gallon. The 1824 Act defined as the volume of a gallon to be that of 10 pounds (4.54kg) of distilled water weighed in air with brass weights with the barometer standing at 30 inches of mercury (102kPa) at a temperature of 62°F (17°C).[18] The 1824 Act went on to give this volume as 277.274 cubic inches (4.54371 litres).[18] The Weights and Measures Act 1963 refined this definition to be the volume of 10 pounds of distilled water of density 0.998859g/mL weighed in air of density 0.001217g/mL against weights of density 8.136g/mL, which works out to 4.546092L.[nb 1] The Weights and Measures Act 1985 defined a gallon to be exactly 4.54609L (approximately 277.4194cuin).[19]
Note: The 1824 Act removed the distinction between liquid and dry measure, specifying instead that the dry quantities shall be unheaped. The metric equivalences shown are approximate.
British apothecaries' volume measures
These measurements were in use from 1826, when the new imperial gallon was defined. For pharmaceutical purposes, they were replaced by the metric system in the United Kingdom on 1 January 1971.[20][21] In the US, though no longer recommended, the apothecaries' system is still used occasionally in medicine, especially in prescriptions for older medications.[22][23]
avoirdupois weight, used for most other purposes; and
apothecaries' weight, now virtually unused since the metric system is used for all scientific purposes.
The distinction between mass and weight is not always clearly drawn. Strictly a pound is a unit of mass, but it is commonly referred to as a weight. When a distinction is necessary, the term pound-force may refer to a unit of force rather than mass. The troy pound (373.2417216g) was made the primary unit of mass by the 1824 Act and its use was abolished in the UK on 1 January 1879,[30] with only the troy ounce (31.1034768g) and its decimal subdivisions retained.[31] The Weights and Measures Act 1855 (18 & 19 Vict. c. 72) made the avoirdupois pound the primary unit of mass.[32] In all the systems, the fundamental unit is the pound, and all other units are defined as fractions or multiples of it.
The plural stone is often used when providing a weight (e.g. "this sack weighs 8 stone").[34] A person's weight is usually quoted in stone 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.
One quarter (literally a quarter of a hundredweight) is equal to two stone or 28 pounds. The term quarter is also used in retail contexts, where it refers to four ounces, i.e. a quarter of a pound. (The 1824 Act defined a quarter as a unit of volume, as above: thus a 'quarter of wheat', 64 gallons, would weigh about 494 lb.[35]).
One imperial hundredweight is equal to eight stone. This is the long hundredweight, 112 pounds, as opposed to the short hundredweight of 100 pounds used in the United States and Canada.[36]
Twenty hundredweight equals a ton (as in the US and Canadian[36] systems). The imperial hundredweight is 12% greater than the US and Canadian one. The imperial ton (or long ton) is 2240 pounds, which is much closer to a tonne (about 2204.6 pounds), compared to the 10.7% smaller North American short ton of 2000 pounds (907.185kg).
The slug, a unit associated with imperial and US customary systems, is a mass that accelerates by 1ft/s2 when a force of one pound (lbf) is exerted on it.[37]
= 1 lb × g/gc (by definition of the pound force[citation needed])
g
≈ 32.17404856ft/s2
gc
≈ 32.17404856lbm⋅ft/lbf⋅s2
∴
1 slug
≈ 32.17404856pounds
Natural equivalents
The 1824 Act of Parliament defined the yard and pound by reference to the prototype standards, and 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 Levelin 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.[4]
Since the Weights and Measures Act 1985, British law defines base imperial units in terms of their metric equivalent. The metric system is routinely used in business and technology within the United Kingdom, with imperial units remaining in widespread use amongst the public.[38] All UK roads use the imperial system except for weight limits, and newer height or width restriction signs give metric alongside imperial.[39]
A baby bottle that measures in three measurement systems—metric, imperial (UK), and US customary
Traders in the UK may 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 imperial units still legally mandated for certain applications such as draught beer and cider,[40] and road-signs.[41] 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 1878, the troy ounce may 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.
Some British people still use one or more imperial units in everyday life for distance (miles, yards, feet, and inches) and some types of volume measurement (especially milk and beer in pints; rarely for canned or bottled soft drinks, or petrol).[38][42]As of February 2021[update], many British people also still use imperial units in everyday life for body weight (stones and pounds for adults, pounds and ounces for babies).[43] Government documents aimed at the public may give body weight and height in imperial units as well as in metric.[44] A survey in 2015 found that many people did not know their body weight or height in both systems.[45] People under the age of 40 preferred the metric system but people aged 40 and over preferred the imperial system.[46] As in other English-speaking countries, including Australia, Canada and the United States, the height of horses is usually measured in hands, standardised to 4 inches (102mm). Fuel consumption for vehicles is commonly stated in miles per gallon (mpg), though official figures always include litres per 100km equivalents and fuel is sold in litres. When sold draught in licensed premises, beer and cider must be sold in pints, half-pints or third-pints.[47] 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 contracts and land registration purposes, the units are always hectares and square metres.[48]
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. Display sizes for screens on television sets and computer monitors are always diagonally measured in inches. Food sold by length or width, e.g. pizzas or sandwiches, is generally sold in inches. Clothing is usually 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.[49]
Pre-packaged products can show both metric and imperial measures, and it is also common to see imperial pack sizes with metric only labels, e.g. a 1lb (454g) tin of Lyle's Golden Syrup is always labelled 454g with no imperial indicator. Similarly most jars of jam and packs of sausages are labelled 454g with no imperial indicator.
India began converting to the metric system from the imperial system 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. By 1962, metric units became "mandatory and exclusive."[50]
Today all official measurements are made in the metric system. 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. Tyre rim diameters are still measured in inches, as used worldwide. 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.[51]
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. All three systems are officially permitted for trade,[52] and in the wider society a mixture of all three systems prevails.
The Chinese system's most commonly used units for length are 里 (lei5), 丈 (zoeng6), 尺 (cek3), 寸 (cyun3), 分 (fan1) 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" (英, jing1) for the imperial system and "Wa" (華, waa4) for the Chinese system. In writing, derived characters are often used, with an additional 口 (mouth) radical to the left of the original Chinese character, for writing imperial units. The most commonly used units are the mile or "li" (哩, li1), the yard or "ma" (碼, maa5), the foot or "chek" (呎, cek3), and the inch or "tsun" (吋, cyun3).
The traditional measure of flat area is the square foot (方呎, 平方呎, fong1 cek3, ping4 fong1 cek3) of the imperial system, which is still in common use for real estate purposes. The measurement of agricultural plots and fields is traditionally conducted in 畝 (mau5) of the Chinese system.
For the measurement of volume, Hong Kong officially uses the metric system, though the gallon (加侖, gaa1 leon4-2) is also occasionally used.
A one US gallon gas can purchased near the US-Canada border showing equivalences in imperial gallons and litresImperial and metric measurements on Canadian canned goods labels. The imperial measurements often take precedence over the metric ones on labels.
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 public road signs and 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.[53][54][55][56] The law requires that measured products (such as fuel and meat) be priced in metric units and an imperial price can be shown if a metric price is present.[57][58] 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. 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. 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. Quebec has implemented metrication more fully. [citation needed] 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, though many English-speaking Canadians give their height and weight in imperial. 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.[59][60][61][62][63] Land is now surveyed and registered in metric units whilst 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. In English-speaking Canada commercial and residential spaces are mostly (but not exclusively) constructed using square feet, while in French-speaking Quebec commercial and residential spaces are constructed in metres and advertised using both square metres and square feet as equivalents. Carpet or flooring tile is purchased by the square foot, but less frequently also in square metres.[64][65] Motor-vehicle fuel consumption is reported in both litres per 100km and statute miles per imperial gallon,[66] 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).[67]
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). 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.
In keeping with the international standard, air navigation is based on nautical units, e.g., the nautical mile, which is neither imperial nor metric, and altitude is measured in imperial feet.[68]
While metrication in Australia has largely ended the official use of imperial units, for particular measurements, 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 5mL.
Newborns are measured in metric at hospitals, but the birth weight and length is sometimes also announced to family and friends in imperial units.
Screen sizes, are frequently advertised in inches instead of or as well as centimetres.
Property size is frequently advertised in acres, but is mostly as square metres.
Navigation is done in nautical miles, and water-based speed limits are in nautical miles per hour.
Historical writing and presentations may include pre-metric units to reflect the context of the era represented.
The illicit drug trade in Australia still often uses imperial measurements, particularly when dealing with smaller amounts closer to end user levels e.g. "8-ball" an 8th of an ounce or 3.5g; cannabis is often traded in ounces ("oz") and pounds ("p")[citation needed]
Firearm barrel length are almost always referred by in inches, ammunition is also still measured in grains and ounces as well as grams.
As a result of cultural transmission of British and American English in Australia, there has also been noted to be a cause for residual use of imperial units of measure.
New Zealand introduced the metric system on 15 December 1976.[69] Aviation was exempt, with altitude and airport elevation continuing to be 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, monitors and phones, and wheel rim sizes for vehicles, are stated in inches, as is the convention in the rest of the world - and a 1992 study found a continued use of imperial units for birth weight and human height alongside metric units.[70]
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 with traditional quantities being retained for goods like butter and sausages, which are sold in 454 grams (1lb) 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. Often signs such as those for bridge height can display both metric and imperial units. Imperial measurements continue to be used colloquially by the general population especially with height and distance measurements such as feet, inches, and acres as well as for weight with pounds and stones still in common use among people of all ages. Measurements such as yards have fallen out of favour with younger generations. Ireland's railways still use imperial measurements for distances and speed signage.[71][72] Property is usually listed in square feet as well as metres also.
Horse racing in Ireland still continues to use stones, pounds, miles and furlongs as measurements.[73]
Bahamas
Imperial measurements remain in general use in the Bahamas.
Legally, both the imperial and metric systems are recognised by the Weights and Measures Act 2006.[74]
Belize
Both imperial units and metric units are used in Belize. Both systems are legally recognized by the National Metrology Act.[75]
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 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.
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.[84]
↑ Jerrard and McNeill, Dictionary of Scientific Units, second edition, Chapman and Hall; cites first appearance in print in Journal of the Institution of Electrical Engineers (G.B.) vol. 1, page 246 (1872).
↑ The exact figure was 6.08ft, but 6ft 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 5fathoms 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.
↑ 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).
1 2 3 "An Act for ascertaining and establishing Uniformity of Weights and Measures (17 June 1824)"(PDF). legislation.gov.uk. 17 June 1824. p.639,640. Archived(PDF) from the original on 20 July 2020. Retrieved 19 January 2020. Two such Gallons shall be a Peck, and Eight such Gallons shall be a Bushel, and Eight such Bushels a Quarter of Corn or other dry Goods, not measured by Heaped Measure.. (The date of coming into effect was 1 May 1825).
↑ imperial gallon. Sizes.com. 25 October 2013. Archived from the original on 14 May 2011. Retrieved 10 July 2019.
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). Archived from the original on 9 July 2018. Retrieved 6 July 2012.
1 2 Kelly, Jon (21 December 2011). "Will British people ever think in metric?". BBC. Archived from the original on 24 April 2012. 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...
↑ "Height and width road signs to display metric and imperial". BBC. 8 November 2014. Archived from the original on 26 February 2017. 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.
↑ Dahlgreen, Will (20 June 2015). "Britain's metric muddle not changing any time soon". Archived from the original on 30 October 2017. Retrieved 29 October 2017. even today [2015] some 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%).
↑ Canada, Government of Canada, Transportation Safety Board of (9 April 1999). "Railway Investigation Report R96W0171". Archived from the original on 6 July 2011. Retrieved 5 March 2011.{{cite web}}: CS1 maint: multiple names: authors list (link)
↑ Parliament of the Bahamas. "Weights and Measures Act 2006". Bahamas Bureau of Standards and Quality. Archived from the original on 2 June 2021. Retrieved 24 September 2021.
↑ Gyi, Ko Ko (18–24 July 2011). "Ditch the viss, govt urges traders". Business and Property. The Myanmar Times. Translated by Thit Lwin. Myanmar. Archived from the original on 20 September 2011. Retrieved 4 March 2023.
↑ "FAQ". MoF.gov.bz. Belize Ministry of Finance. Archived from the original on 23 January 2008. 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)
↑ Metschies, Gerhard P. (6 September 2005). "International Fuel Prices 2005"(PDF). International-Fuel-Prices.com. German Technical Cooperation. p.96. Archived from the original(PDF) on 7 February 2007. Retrieved 15 January 2008.
Metrication or metrification is the act or process of converting to the metric system of measurement. All over the world, countries have transitioned from local and traditional units of measurement to the metric system. This process began in France during the 1790s, and has persistently advanced over two centuries, accumulating into 95% of the world officially only using the modern metric system. Nonetheless, this also highlights that certain countries and sectors are either still transitioning or have chosen not to fully adopt the metric system.
United States customary units form a system of measurement units commonly used in the United States and most U.S. territories, since being standardized and adopted in 1832. The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures was overhauled in 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are significant differences between the systems.
In recipes, quantities of ingredients may be specified by mass, by volume, or by count.
Troy weight is a system of units of mass that originated in 15th-century Kingdom of England and is primarily used in the precious metals industry. The troy weight units are the grain, the pennyweight, the troy ounce, and the troy pound. The troy grain is equal to the grain unit of the avoirdupois system, but the troy ounce is heavier than the avoirdupois ounce, and the troy pound is lighter than the avoirdupois pound. One troy ounce equals exactly 31.1034768 grams.
A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and apothecaries' systems, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single ideal seed of a cereal. From the Bronze Age into the Renaissance, the average masses of wheat and barley grains were part of the legal definitions of units of mass. Expressions such as "thirty-two grains of wheat, taken from the middle of the ear" appear to have been ritualistic formulas. Another source states that it was defined such that 252.458 units would balance 1 cubic inch (16 cm3) of distilled water at an ambient air-water pressure and temperature of 30 inches of mercury (100 kPa) and 62 °F (17 °C) respectively. Another book states that Captain Henry Kater, of the British Standards Commission, arrived at this value experimentally.
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 although some of them still also have traditional units called pints, the volume varies by regional custom.
The minim is a unit of volume in both the imperial and U.S. customary systems of measurement. Specifically it is 1⁄60 of a fluid drachm or 1⁄480 of a fluid ounce.
The long ton, also known as the imperial ton or displacement ton, is a measurement unit equal to 2,240 pounds (1,016.047 kg). It 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 13th century. It is used in the United Kingdom and several other Commonwealth of Nations countries alongside the mass-based tonne defined in 1799, as well as in the United States for bulk commodities.
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. U.S. customary units have been defined in terms of metric units since the 19th century, and the SI has been the "preferred system of weights and measures for United States trade and commerce" since 1975 according to United States law. However, conversion was not mandatory and many industries chose not to convert, and U.S. customary units remain in common use in many industries as well as in governmental use. There is government policy and metric (SI) program to implement and assist with metrication, however there is major social resistance for further metrication.
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.
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 prescriptions 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 of 20 grains each. 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 units of measurement, also known as a system of units or 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. Instances in use include the International System of Units or SI, the British imperial system, and the United States customary system.
English units were the units of measurement 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.
Metrication in Canada began in 1970 and ceased in 1985. 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 and everyday life today. 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 strong public opposition to metrication during the transition period.
Metrication, the process of introducing the metric system of measurement in place of imperial units, has made steady progress in the United Kingdom since the mid-20th century but today remains equivocal and varies by context.
Metrication, or the conversion to a measurement system based on the International System of Units (SI), occurred in India 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 in 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, metricate, reissue all government publications and laws, and change the education systems to metric.
Metrication in the Republic of Ireland happened mostly in the 20th century and was officially completed in 2005, with a few exceptions.
Both the British imperial measurement system and United States customary systems of measurement derive from earlier English unit systems used prior to 1824 that were the result of a combination of the local Anglo-Saxon units inherited from Germanic tribes and Roman units.
The imperial and US customary measurement systems 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.
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