|Unit system||English unit|
|Symbol||mi or m|
|1 mi in ...||... is equal to ...|
|SI units||1609.344 m|
|nautical units||0.86898 nmi|
The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959.
With qualifiers, "mile" is also used to describe or translate a wide range of units derived from or roughly equivalent to the Roman mile, such as the nautical mile (now 1.852 km exactly), the Italian mile (roughly 1.852 km), and the Chinese mile (now 500 m exactly). The Romans divided their mile into 5,000 Roman feet but the greater importance of furlongs in pre-modern England meant that the statute mile was made equivalent to 8 furlongs or 5,280 feet in 1593. This form of the mile then spread to the British-colonized nations some of which continue to employ the mile. The US Geological Survey now employs the metre for official purposes but legacy data from its 1927 geodetic datum has meant that a separate US survey mile (6336/ km) continues to see some use. While most countries replaced the mile with the kilometre when switching to the International System of Units, the international mile continues to be used in some countries, such as Liberia, the United Kingdom, the United States, and a number of countries with fewer than one million inhabitants, most of which are UK or US territories, or have close historical ties with the UK or US.
The mile was usually abbreviated m. in the past in the USA but is now written as mi to avoid confusion with the SI metre. In the United Kingdom, road signs still abbreviate mile to "m" and yard to "yds". However, derived units, such as miles per hour or miles per gallon, continue to be abbreviated as mph and mpg, respectively.
The modern English word mile derives from Middle English myle and Old English mīl, which was cognate with all other Germanic terms for "miles". These derived from the nominal ellipsis form of mīlle passus (mile) or mīlia passuum (miles), the Roman mile of one thousand paces.
The present international mile is usually what is understood by the unqualified term "mile". When this distance needs to be distinguished from the nautical mile, the international mile may also be described as a "land mile" or "statute mile". yards. Under American law, however, the "statute mile" refers to the US survey mile. Foreign and historical units translated into English as miles usually employ a qualifier to describe the kind of mile being used but this may be omitted if it is obvious from the context, such as a discussion of the 2nd-century Antonine Itinerary describing its distances in terms of "miles" rather than "Roman miles".In British English, the "statute mile" may refer to the present international miles or to any other form of English mile since the 1593 Act of Parliament, which set it as a distance of 1,760
The mile has been variously abbreviated—with and without a trailing period—as m, M, ml, and mi.The American National Institute of Standards and Technology now uses and recommends mi to avoid confusion with the SI metre (m) and millilitre (ml). However, derived units such as miles per hour or miles per gallon continue to be abbreviated as mph and mpg rather than mi/h and mi/gal. In the United Kingdom road signs use m as the abbreviation for mile though height and width restrictions also use m as the abbreviation for the metre, which may be displayed alongside feet and inches. The BBC style holds that "There is no acceptable abbreviation for 'miles'" and so it should be spelled out when used in describing areas.
The Roman mile ( mille passus ,lit. "thousand paces"; abbr. m.p.; also milia passuum and mille) consisted of a thousand paces as measured by every other step—as in the total distance of the left foot hitting the ground 1,000 times. The ancient Romans, marching their armies through uncharted territory, would often push a carved stick in the ground after each 1,000 paces. Well-fed and harshly driven Roman legionaries in good weather thus created longer miles. The distance was indirectly standardised by Agrippa's establishment of a standard Roman foot (Agrippa's own) in 29 BC, and the definition of a pace as 5 feet. An Imperial Roman mile thus denoted 5,000 Roman feet. Surveyors and specialised equipment such as the decempeda and dioptra then spread its use.
In modern times, Agrippa's Imperial Roman mile was empirically estimated to have been about 1,617 yards (1,479 m) in length.
In Hellenic areas of the Empire, the Roman mile (Greek : μίλιον, mílion) was used beside the native Greek units as equivalent to 8 stadia of 600 Greek feet. The mílion continued to be used as a Byzantine unit and was also used as the name of the zero mile marker for the Byzantine Empire, the Milion, located at the head of the Mese near Hagia Sophia.[ citation needed ]
The Roman mile also spread throughout Europe, with its local variations giving rise to the different units below.[ citation needed ]
Also arising from the Roman mile is the milestone. All roads radiated out from the Roman Forum throughout the Empire – 50,000 (Roman) miles of stone-paved roads. At every mile was placed a shaped stone. Originally these were stone obelisks made from granite, marble, or whatever local stone was available. On these was carved a Roman numeral, indicating the number of miles from the centre of Rome – the Forum. Hence, one always knew how far one was from Rome.
The Italian mile (miglio, pl. miglia) was traditionally considered a direct continuation of the Roman mile, equal to 1000 paces, although its actual value over time or between regions could vary greatly. It was often used in international contexts from the Middle Ages into the 17th century and is thus also known as the "geographical mile", although the geographical mile is now a separate standard unit.
The Arabic mile (الميل, al-mīl) was not the common Arabic unit of length; instead, Arabs and Persians traditionally used the longer parasang or "Arabic league". The Arabic mile was, however, used by medieval geographers and scientists and constituted a kind of precursor to the nautical or geographical mile. It extended the Roman mile to fit an astronomical approximation of 1 arcminute of latitude measured directly north-and-south along a meridian. Although the precise value of the approximation remains disputed, it was somewhere between 1.8 and 2.0 km.
The "old English mile" of the medieval and early modern periods varied but seems to have measured about 1.3 international miles (2.1 km). The English long continued the Roman computations of the mile as 5000 feet, 1000 paces, or 8 longer divisions, which they equated with their "furrow's length" or furlong.
The origins of English units are "extremely vague and uncertain", I was said to have made a new standard in 1101 based on his own arm. Following the issuance of Magna Carta, the barons of Parliament directed John and his son to keep the king's standard measure (Mensura Domini Regis) and weight at the Exchequer, which thereafter verified local standards until its abolition in the 19th century. New brass standards are known to have been constructed under Henry VII and Elizabeth I.but seem to have been a combination of the Roman system with native British and Germanic systems both derived from multiples of the barleycorn. Probably by the reign of Edgar in the 10th century, the nominal prototype physical standard of English length was an arm-length iron bar (a yardstick) held by the king at Winchester; the foot was then one-third of its length. Henry
Arnold's c. 1500Customs of London recorded a mile shorter than previous ones, coming to 0.947 international miles or 1.524 km.
The English statute mile was established by a Weights and Measures Act of Parliament in 1593 during the reign of Queen Elizabeth I. The act on the Composition of Yards and Perches had shortened the length of the foot and its associated measures, causing the two methods of determining the mile to diverge. Owing to the importance of the surveyor's rod in deeds and surveying undertaken under Henry VIII, decreasing the length of the rod by 1⁄11 would have amounted to a significant tax increase. Parliament instead opted to maintain the mile of 8 furlongs (which were derived from the rod) and to increase the number of feet per mile from the old Roman value. The applicable passage of the statute reads: "A Mile shall contain eight Furlongs, every Furlong forty Poles, and every Pole shall contain sixteen Foot and an half." The statute mile therefore contained 5,280 feet or 1,760 yards. The distance was not uniformly adopted. Robert Morden had multiple scales on his 17th-century maps which included continuing local values: his map of Hampshire, for example, bore two different "miles" with a ratio of 1 : 1.23 and his map of Dorset had three scales with a ratio of 1 : 1.23 : 1.41. In both cases, the traditional local units remained longer than the statute mile.
The Welsh mile (milltir or milldir) was 3 miles and 1470 yards long (6.17 km). It comprised 9000 paces (cam), each of 3 Welsh feet (troedfedd) of 9 inches (modfeddi). (The Welsh inch is usually reckoned as equivalent to the English inch.) Along with other Welsh units, it was said to have been codified under Dyfnwal the Bald and Silent and retained unchanged by Hywel the Good. Along with other Welsh units, it was discontinued following the conquest of Wales by the English under Edward I in the 13th century.
The Scots mile was longer than the English mile, (Scots) furlongs divided into 320 falls or faws (Scots rods). It varied from place to place but the most accepted equivalencies are 1,976 Imperial yards (1.123 statute miles or 1.81 km).as mentioned by Robert Burns in the first verse of his poem "Tam o' Shanter". It comprised 8
It was legally abolished three times: first by a 1685 act of the Scottish Parliament,again by the 1707 Treaty of Union with England, and finally by the Weights and Measures Act 1824. It had continued in use as a customary unit through the 18th century but had become obsolete by its final abolition.
The Irish mile (míle or míle Gaelach) measured 2240 yards: approximately 1.27 statute miles or 2.048 kilometres. 7 yards (6.4 m) as opposed to the English rod of 5.5 yards (5.0 m).It was used in Ireland from the 16th century plantations until the 19th century, with residual use into the 20th century. The units were based on "English measure" but used a linear perch measuring
The international mile is precisely equal to 1.609344 km (or 25146/ km as a fraction). It was established as part of the 1959 international yard and pound agreement reached by the United States, the United Kingdom, Canada, Australia, New Zealand, and Union of South Africa, which resolved small but measurable differences that had arisen from separate physical standards each country had maintained for the yard. As with the earlier statute mile, it continues to comprise 1,760 yards or 5,280 feet.
The old Imperial value of the yard was used in converting measurements to metric values in India in a 1976 Act of the Indian Parliament.However, the current National Topographic Database of the Survey of India is based on the metric WGS-84 datum, which is also used by the Global Positioning System.
The difference from the previous standards was 2 ppm, or about 3.2 millimetres (1⁄8 inch) per mile. The U.S. standard was slightly longer and the old Imperial standards had been slightly shorter than the international mile. When the international mile was introduced in English-speaking countries, the basic geodetic datum in America was the North American Datum of 1927 (NAD27). This had been constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893, with 1 foot = 1200/ metres and the definition was retained for data derived from NAD27, but renamed the U.S. survey foot to distinguish it from the international foot.
The exact length of the land mile varied slightly among English-speaking countries until the international yard and pound agreement in 1959 established the yard as exactly 0.9144 metres, giving a mile of exactly 1,609.344 metres. The U.S. adopted this international mile for most purposes, but retained the pre-1959 mile for some land-survey data, terming it the U. S. survey mile. In the United States, statute mile normally refers to the survey mile, about 3.219 mm (1⁄8 inch) longer than the international mile (the international mile is exactly 0.0002% less than the U.S. survey mile).
While most countries abandoned the mile when switching to the metric system, the international mile continues to be used in some countries, such as Liberia, Myanmar,the United Kingdom and the United States. It is also used in a number of territories with less than a million inhabitants, most of which are U.K. or U.S. territories, or have close historical ties with the U.K. or U.S.: American Samoa, Bahamas, Belize, British Virgin Islands, Cayman Islands, Dominica, Falkland Islands, Grenada, Guam, The N. Mariana Islands, Samoa, St. Lucia, St. Vincent & The Grenadines, St. Helena, St. Kitts & Nevis, the Turks & Caicos Islands, and the U.S. Virgin Islands. The mile is even encountered in Canada, though this is predominantly in rail transport and horse racing, as the roadways have been metricated since 1977. The Republic of Ireland replaced miles with kilometres, and speeds in miles per hour with kilometres per hour, gradually. The process was completed in 2005.
The U.S. survey mile is 5,280 survey feet, or about 1,609.347 metres. In the United States, the term statute mile formally refers to the survey mile, but for most purposes, the difference between the survey mile and the international mile is insignificant—one international mile is 0.999998 U.S. survey miles—so statute mile can be used for either. But in some cases, such as in the U.S. State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles, the accumulated difference can be significant, so it is important to note that the reference is to the U.S. survey mile.
The United States redefined its yard in 1893, and this resulted in U.S. and Imperial measures of distance having very slightly different lengths.
The North American Datum of 1983 (NAD83), which replaced the NAD27, is defined in metres. State Plane Coordinate Systems were then updated, but the National Geodetic Survey left individual states to decide which (if any) definition of the foot they would use. All State Plane Coordinate Systems are defined in metres, and 42 of the 50 states only use the metre-based State Plane Coordinate Systems. However, eight states also have State Plane Coordinate Systems defined in feet, seven of them in U.S. Survey feet and one in international feet.
State legislation in the U.S. is important for determining which conversion factor from the metric datum is to be used for land surveying and real estate transactions, even though the difference (2 ppm) is hardly significant, given the precision of normal surveying measurements over short distances (usually much less than a mile). Twenty-four states have legislated that surveying measures be based on the U.S. survey foot, eight have legislated that they be based on the international foot, and eighteen have not specified which conversion factor to use.
In October 2019, U.S. National Geodetic Survey and National Institute of Standards and Technology announced their joint intent to retire the U.S. survey foot and U.S. survey mile, as permitted by their 1959 decision, with effect from the end of 2022.
The nautical mile was originally defined as one minute of arc along a meridian of the Earth.Navigators use dividers to step off the distance between two points on the navigational chart, then place the open dividers against the minutes-of-latitude scale at the edge of the chart, and read off the distance in nautical miles. The Earth is not perfectly spherical but an oblate spheroid, so the length of a minute of latitude increases by 1% from the equator to the poles. Using the WGS84 ellipsoid, the commonly accepted Earth model for many purposes today, one minute of latitude at the WGS84 equator is 6,046 feet and at the poles is 6,107.5 feet. The average is about 6,076 feet (about 1,852 metres or 1.15 statute miles).
In the United States, the nautical mile was defined in the 19th century as 6,080.2 feet (1,853.249 m), whereas in the United Kingdom, the Admiralty nautical mile was defined as 6,080 feet (1,853.184 m) and was about one minute of latitude in the latitudes of the south of the UK. Other nations had different definitions of the nautical mile, but it is now internationally defined to be exactly 1,852 metres (6,076.11548556 feet).
The nautical mile per hour is known as the knot. Nautical miles and knots are almost universally used for aeronautical and maritime navigation, because of their relationship with degrees and minutes of latitude and the convenience of using the latitude scale on a map for distance measuring.
The data mile is used in radar-related subjects and is equal to 6,000 feet (1.8288 kilometres). μs and the radar nautical mile is 12.4 μs.The radar mile is a unit of time (in the same way that the light year is a unit of distance), equal to the time required for a radar pulse to travel a distance of two miles (one mile each way). Thus, the radar statute mile is 10.8
The geographical mile is based upon the length of a meridian of latitude. The German geographical mile (geographische Meile) was previously 1⁄15° of latitude (7.4127 km).
Cities in the continental United States often have streets laid out by miles. Detroit, Indianapolis, Chicago, Phoenix, Philadelphia, Las Vegas, Los Angeles, and Miami, are several examples. Typically the largest streets are about a mile apart, with others at smaller intervals. In the Manhattan borough of New York City "streets" are close to 20 per mile, while the major numbered "avenues" are about six per mile. (Centerline to centerline, 42nd Street to 22nd Street is supposed to be 5250 feet while 42nd Street to 62nd Street is supposed to be [ clarification needed ] 5276 ft 8 in.)[ citation needed ]
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The informal term "metric mile" is used in some countries, in sports such as track and field athletics and speed skating, to denote a distance of 1,500 metres (0.932 miles). The 1500 meters is the premier middle distance running event in Olympic sports. In United States high-school competition, the term is sometimes used for a race of 1,600 metres (0.994 miles).
The Scandinavian mile (mil) remains in common use in Norway and Sweden, where it has meant precisely 10 km since metrication in 1889. It is used in informal situations and in measurements of fuel consumption, which are often given as litres per mil. In formal situations (such as official road signs) and where confusion may occur with international miles, it is avoided in favour of kilometres.
The Swedish mile was standardised as 36,000 Swedish feet or 10.687 km in 1649; before that it varied by province from about 6 to 14.485 km.
Before metrication, the Norwegian mile was 11.298 km.
The traditional Finnish peninkulma was translated as mil in Swedish and also set equal to 10 km during metrication in 1887, but is much less commonly used.
A comparison of the different lengths for a "mile", in different countries and at different times in history, is given in the table below. Leagues are also included in this list because, in terms of length, they fall in between the short West European miles and the long North, Central and Eastern European miles.
|Length (m)||Name||Country used||From||To||Definition||Remarks|
|960–1,152||talmudic mil||Palestine||Biblical and Talmudic units of measurement|
|1,480||mille passus, milliarium||Roman Empire||Ancient Roman units of measurement|
|1,609.3426||(statute) mile||Great Britain||1592||1959||1,760 yards||Over the course of time, the length of a yard changed several times and consequently so did the English, and from 1824, the imperial mile. The statute mile was introduced in 1592 during the reign of Queen Elizabeth I|
|1,609.344||mile||some Anglosaxon countries||1959||today||1760 yards||In 1 July 1959 the imperial mile was standardized to an exact length in metres|
|1,609.3472||(statute) mile||United States||1893||today||1,760 yards||From 1959 also called the U.S. Survey Mile. From then its only utility has been land survey, before it was the standard mile. From 1893 its exact length in metres was: 3600/ × 1760|
|1,852||nautical mile||international||today||approx. 1 minute of arc||Measured at a circumference of 40,000 km. Abbreviation: NM, nm|
|1,852.3||(for comparison)||1 meridian minute|
|1,855.4||(for comparison)||1 equatorial minute||Although the NM was defined on the basis of the minute, it varies from the equatorial minute, because at that time the circumference of the equator could only be estimated at 40,000 km.|
|2,220||Gallo-Roman league||Gallo-Roman culture||1.5 miles||Under the reign of Emperor Septimius Severus, this replaced the Roman mile as the official unit of distance in the Gallic and Germanic provinces, although there were regional and temporal variations.|
|3,898||French lieue (post league)||France||2,000 "body lengths"|
|4,000||general or metric league|
|4,190||legue||Mexico||= 2,500 tresas = 5,000 varas|
|4,444.8||landleuge||1⁄25° of a circle of longitude|
|4,452.2||lieue commune||France||Units of measurement in France before the French Revolution|
|4,513||legua||Chile, (Guatemala, Haiti)||= 36 cuadros = 5400 varas|
|4,828||English land league||England||3 miles|
|Germanic rasta, also doppelleuge|
|5,196||legua||Bolivia||= 40 ladres|
|5,152||legua argentina||Argentina, Buenos Aires||= 6,000 varas|
|5,556||Seeleuge (nautical league)||1⁄20° of a circle of longitude |
3 nautical miles
|5,570||legua||Spain and Chile||Spanish customary units|
|5,572||legua||Colombia||= 3 Millas|
|5,572.7||legue||Peru||= 20,000 feet|
|Spain||= 3 millas = 15,000 feet|
|5,590||légua||Brazil||= 5,000 varas = 2,500 bracas|
|5,685||Fersah (Turkish league)||Ottoman Empire||1933||4 Turkish miles||Derived from Persian Parasang .|
|6,170||milltir||Wales||13thC||9000 camau ( = 27 000 troedfeddi = 243 000 inches)||Eclipsed by the conquest of Wales by Edward I|
|6,197||légua antiga||Portugal||= 3 milhas = 24 estadios|
new league, since 1766
|Spain||= 8,000 varas|
(state survey mile)
|7,409||(for comparison)||4 meridian minutes|
|7,419.2||Kingdom of Hanover|
|7,419.4||Duchy of Brunswick|
|7,420.439||geographic mile||1⁄15 equatorial grads [ dubious ]|
|7,421.6||(for comparison)||4 equatorial minutes|
|7,467.6||Russia||7 verst||Obsolete Russian units of measurement|
|7,500||kleine / neue Postmeile|
(small/new postal mile)
|Saxony||1840||German Empire, North German Confederation, Grand Duchy of Hesse, Russia|
(German state mile)
|Denmark, Hamburg, Prussia||primarily for Denmark defined by Ole Rømer|
|Austro-Hungary||Austrian units of measurement|
|9,062||mittlere Post- / Polizeimeile|
(middle post mile or police mile)
|9,206.3||Electorate of Hesse|
|9,261.4||(for comparison)||5 meridian minutes|
|9,277||(for comparison)||5 equatorial minutes|
(old state mile)
(old state mile)
|10,000||metric mile, Scandinavian mile||Norway, Sweden||still commonly used today, e. g. for road distances.; equates to the myriametre|
|10,688.54||mil||Sweden||1889||In normal speech, "mil" means a Scandinavian mile of 10 km.|
|11,113.7||(for comparison)||6 meridian minutes|
|11,132.4||(for comparison)||6 equatorial minutes|
|11,299||mil||Norway||was equivalent to 3000 Rhenish rods.|
Even in English-speaking countries that have moved from the Imperial to the metric system (for example, Australia, Canada, and New Zealand), the mile is still used in a variety of idioms. These include:
The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong, which is exactly equal to 10 square chains, 1⁄640 of a square mile, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare. Based upon the International yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 square metres. One recognised symbol for the acre is ac, but the word 'acre' is also used as the symbol.
A furlong is a measure of distance in imperial units and U.S. customary units equal to one eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, 10 chains or approximately 201 meters.
The inch is a unit of length in the (British) imperial and United States customary systems of measurement. It is equal to 1⁄36 yard or 1⁄12 of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb.
The imperial system of units, imperial system or imperial units 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. The imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825. 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 but 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.
A nautical mile is a unit of measurement used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as one minute of latitude along any line of longitude. Today the international nautical mile is defined as exactly 1852 metres. The derived unit of speed is the knot, one nautical mile per hour.
United States customary units are a system of measurements commonly used in the United States. The United States customary system developed from English units which were in use in the British Empire before the U.S. became an independent country. However, the United Kingdom's system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U.S. units are essentially similar to their imperial counterparts, there are significant differences between the systems.
The yard is an English unit of length, in both the British imperial and US customary systems of measurement, that comprises 3 feet or 36 inches. 1,760 yards is equal to 1 mile.
The mile is an imperial and US unit of measure for an area equal to the area of a square with a side length of one statute mile. It should not be confused with miles square, which refers to a square region with each side having the specified length. For instance, 20 miles square has an area equal to 400 square miles; a rectangle of 10 × 40 miles likewise has an area of 400 square miles, but it is not 20 miles square.
A fathom is a unit of length in the imperial and the U.S. customary systems equal to 6 feet (1.8288 m), used especially for measuring the depth of water. The fathom is not an International Standard (SI) unit, nor is it accepted internationally as a non-SI unit. However it is historically the most frequently employed maritime measure of depth in the English speaking world.
The foot is a unit of length in the imperial and US customary systems of measurement. Since the International Yard and Pound Agreement of 1959, one foot is defined as 0.3048 meter exactly. In customary and imperial units, one foot comprises 12 inches and three feet comprise one yard.
The knot is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h. The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE); kt is also common, especially in aviation, where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. The knot is used in meteorology, and in maritime and air navigation. A vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.
A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are U.S. customary units in the United States and metric units elsewhere. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.
The rod or perch or pole is a surveyor's tool and unit of length of various historical definitions, often between 3 and 8 meters. In modern US customary units it is defined as 16 1⁄2 US survey feet, equal to exactly 1⁄320 of a surveyor's mile, or one-fourth of a surveyor's chain, and is approximately 5.0292 meters. The rod is useful as a unit of length because whole number multiples of it can form one acre of square measure. The 'perfect acre' is a rectangular area of 43,560 square feet, bounded by sides 660 feet long and 66 feet wide or, equivalently, 40 rods and 4 rods. An acre is therefore 160 square rods.
The chain is a unit of length equal to 66 feet. It is subdivided into 100 links or 4 rods. There are 10 chains in a furlong, and 80 chains in one statute mile. In metric terms, it is 20.1168 m long. By extension, chainage is the distance along a curved or straight survey line from a fixed commencing point, as given by an odometer.
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
A league is a unit of length. It was common in Europe and Latin America, but is no longer an official unit in any nation. The word originally meant the distance a person could walk in an hour. Since the Middle Ages, many values have been specified in several countries.
A pace is a unit of length consisting either of one normal walking step, or of a double step, returning to the same foot. Like other traditional measurements, paces started as informal units but have since been standardized, often with the specific length set according to a typical brisk or military marching stride.
English units are 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 earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction, and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable 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.