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The yard (symbol: yd) is an English unit of
length Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most systems of measurement a Base unit (measurement), base unit for length is chosen, ...
in both the British imperial and US customary
systems of measurement 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 defi ...
equalling 3  feet or 36 
inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...
es. Since 1959 it has been by international agreement standardized as exactly 0.9144 
meter The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
. A distance of 1,760 yards is equal to 1
mile The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a imperial unit, British imperial unit and United States customary unit of length; both are based on the older English unit of Unit of length, le ...
. The theoretical US survey yard is very slightly longer.


Name

The term, ''yard'' derives from the
Old English Old English ( or , or ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the Early Middle Ages. It developed from the languages brought to Great Britain by Anglo-S ...
, etc., which was used for
branch A branch, also called a ramus in botany, is a stem that grows off from another stem, or when structures like veins in leaves are divided into smaller veins. History and etymology In Old English, there are numerous words for branch, includ ...
es, staves and measuring rods. It is first attested in the late 7th century
laws Law is a set of rules that are created and are law enforcement, enforceable by social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a Socia ...
of
Ine of Wessex Ine or Ini (died in or after 726) was King of Wessex from 689 to 726. At Ine's accession, his kingdom dominated much of what is now southern England. However, he was unable to retain the territorial gains of his predecessor, Cædwalla of Wessex ...
, wherein the "yard of land" mentioned is the yardland, an old English unit of tax assessment equal to   hide. Around the same time the
Lindisfarne Gospels The Lindisfarne Gospels (London, British Library Cotton MS Nero D.IV) is an illuminated manuscript gospel book probably produced around the years 715–720 in the monastery at Lindisfarne, off the coast of Northumberland, which is now in the Bri ...
account of the messengers from John the Baptist in the
Gospel of Matthew The Gospel of Matthew is the first book of the New Testament of the Bible and one of the three synoptic Gospels. It tells the story of who the author believes is Israel's messiah (Christ (title), Christ), Jesus, resurrection of Jesus, his res ...
used it for a branch swayed by the wind. In addition to the yardland, Old and
Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman Conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English pe ...
both used their forms of "yard" to denote the surveying lengths of or , used in computing
acre The acre ( ) is a Unit of measurement, unit of land area used in the Imperial units, British imperial and the United States customary units#Area, United States customary systems. It is traditionally defined as the area of one Chain (unit), ch ...
s, a distance now usually known as the " rod". A unit of three English feet is attested in a statute of ( see below), but there it is called an ell (,  " arm"), a separate and usually longer unit of around . The use of the word ‘yard’ ( or ) to describe this length is first attested in William Langland's poem on
Piers Plowman ''Piers Plowman'' (written 1370–86; possibly ) or ''Visio Willelmi de Petro Ploughman'' (''William's Vision of Piers Plowman'') is a Middle English allegorical narrative poem by William Langland. It is written in un-rhymed, alliterative ...
. The usage seems to derive from the
prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototype ...
standard rods held by the king and his magistrates ( see below). The word 'yard' is a
homonym In linguistics, homonyms are words which are either; '' homographs''—words that mean different things, but have the same spelling (regardless of pronunciation), or '' homophones''—words that mean different things, but have the same pronunciat ...
of 'yard' in the sense of an enclosed area of land. This second meaning of 'yard' has an
etymology Etymology ( ) is the study of the origin and evolution of words—including their constituent units of sound and meaning—across time. In the 21st century a subfield within linguistics, etymology has become a more rigorously scientific study. ...
related to the word ‘garden’ and is not related to the unit of measurement. In
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
the yard is colloquially known as a guz, which equals 3 feet.


History


Origin

The origin of the yard measure is uncertain. Both the Romans and the Welsh used multiples of a shorter
foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...
, but  
Roman feet The units of measurement of ancient Rome were generally consistent and well documented. Length The basic unit of Roman linear measurement was the ''pes'' (plural: ''pedes'') or Roman foot. Investigation of its relation to the English foot goes ...
was a " step" () and 3  Welsh feet was a " pace" (). The
Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the linguistic reconstruction, reconstructed proto-language of the Germanic languages, Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from ...
cubit The cubit is an ancient unit of length based on the distance from the elbow to the tip of the middle finger. It was primarily associated with the Sumerians, Egyptians, and Israelites. The term ''cubit'' is found in the Bible regarding Noah ...
or arm's-length has been reconstructed as *''alinô'', which developed into the
Old English Old English ( or , or ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the Early Middle Ages. It developed from the languages brought to Great Britain by Anglo-S ...
,
Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman Conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English pe ...
, and modern ell of . This has led some to derive the yard of three English feet from pacing; others from the ell or cubit; and still others from Henry I's arm standard ( see below). Based on the etymology of the other "yard", some suggest it originally derived from the girth of a person's waist, while others believe it originated as a cubic measure. One official British report writes:


From ell to yard

The earliest record of a prototype measure is the statute II Edgar Cap. 8 (AD 959  963), which survives in several variant manuscripts. In it,
Edgar the Peaceful Edgar (or Eadgar; 8 July 975), known sometimes as Edgar the Peacemaker or the Peaceable, was King of the English from 959 until his death in 975. He became king of all England on his brother Eadwig's death. He was the younger son of King Edm ...
directed the
Witenagemot The witan () was the king's council in the Anglo-Saxon government of England from before the 7th century until the 11th century. It comprised important noblemen, including ealdormen, thegns, and bishops. Meetings of the witan were sometimes ...
at Andover that "the measure held at
Winchester Winchester (, ) is a City status in the United Kingdom, cathedral city in Hampshire, England. The city lies at the heart of the wider City of Winchester, a local government Districts of England, district, at the western end of the South Downs N ...
" should be observed throughout his realm. (Some manuscripts read "at
London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...
and at Winchester".) The statutes of William I similarly refer to and uphold the standard measures of his predecessors without naming them.
William of Malmesbury William of Malmesbury (; ) was the foremost English historian of the 12th century. He has been ranked among the most talented English historians since Bede. Modern historian C. Warren Hollister described him as "a gifted historical scholar and a ...
's '' Deeds of the Kings of England'' records that during the reign of Henry I (1100–1135), "the measure of his arm was applied to correct the false ell of the traders and enjoined on all throughout England." The folktale that the length was bounded by the king's nose was added some centuries later. Charles Moore Watson dismisses William's account as "childish", but William was among the most conscientious and trustworthy medieval historians. The French " king's foot" was supposed to have derived from
Charlemagne Charlemagne ( ; 2 April 748 – 28 January 814) was List of Frankish kings, King of the Franks from 768, List of kings of the Lombards, King of the Lombards from 774, and Holy Roman Emperor, Emperor of what is now known as the Carolingian ...
, and the English kings subsequently repeatedly intervened to impose shorter units with the aim of increasing tax revenue. The earliest surviving definition of this shorter unit appears in the Act on the Composition of Yards and Perches, one of the statutes of uncertain date tentatively dated to the reign of Edward I or II . Its wording varies in surviving accounts. One reads:
It is ordained that 3 grains of barley dry and round do make an
inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...
, 12 inches make 1
foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...
, 3 feet make 1 yard, 5 yards and a half make a perch, and 40 perches in length and 4 in breadth make an
acre The acre ( ) is a Unit of measurement, unit of land area used in the Imperial units, British imperial and the United States customary units#Area, United States customary systems. It is traditionally defined as the area of one Chain (unit), ch ...
.
The
Liber Horn ''Liber Horn'' is a book completed in 1311 by Andrew Horn. The National Archives (the official archive of the UK government) describes it as "a compilation of charters, statutes and customs". It is thought to have been a compilation of two separ ...
compilation (1311) includes that statute with slightly different wording and adds:
And be it remembered that the
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
yard of our Lord the King containeth 3 feet and no more, and a foot ought to contain 12
inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...
es by the right measure of this yard measured, to wit, the 36th part of this yard rightly measured maketh 1 inch neither more nor less and 5 yards and a half make a perch that is 16 feet and a half measured by the aforesaid yard of our Lord the King.
In some early books, this act was appended to another statute of uncertain date titled the Statute for the Measuring of Land. The act was not repealed until the Weights and Measures Act 1824.


Yard and inch

In a law of 1439 ( 18 Hen. 6. c. 16) the sale of cloth by the "yard and handful" was abolished, and the "yard and inch" instituted (see ell).
There shall be but one Measure of Cloth through the Realm by the Yard and the Inch, and not by the Yard and Handful, according to the London Measure.
According to Connor, cloth merchants had previously sold cloth by the yard and handful to evade high taxes on cloth (the extra handful being essentially a black-market transaction). Enforcement efforts resulted in cloth merchants switching over to the yard and inch, at which point the government gave up and made the yard and inch official. In 1552, the yard and inch for cloth measurement was again sanctioned in law ( 5 & 6 Edw. 6. c. 6. ''An Act for the true making of Woolen Cloth.'') The yard and inch for cloth measurement was also sanctioned again in legislation of 1557–1558 ( 4 & 5 Ph. & M. c. 5. ''An act touching the making of woolen clothes.'' par. IX.)
IX. Item, That every ordinary kersie mentioned in the said act shall contain in length in the water betwixt xvi. and xvii. yards, yard and inch; and being well scoured thicked, milled, dressed and fully dried, shall weigh nineteen pounds the piece at the least:...
As recently as 1593, the same principle is found mentioned once again ( 35 Eliz. 1. c. 10 ''An act for the reformation of sundry abuses in clothes, called Devonshire kerjies or dozens, according to a proclamation of the thirty-fourth year of the reign of our sovereign lady the Queen that now is.'' par. III.)
(2) and each and every of the same Devonshire kersies or dozens, so being raw, and as it cometh forth off the weaver's loom (without racking, stretching, straining or other device to encrease the length thereof) shall contain in length between fifteen and sixteen yards by the measure of yard and inch by the rule,...


Physical standards

One of the oldest yard-rods in existence is the clothyard of the Worshipful Company of Merchant Taylors. It consists of a hexagonal iron rod in diameter and short of a yard, encased within a silver rod bearing the hallmark 1445. In the early 15th century, the Merchant Taylors Company was authorized to "make search" at the opening of the annual St. Bartholomew's Day Cloth Fair. In the mid-18th century, Graham compared the standard yard of the Royal Society to other existing standards. These were a "long-disused" standard made in 1490 during the reign of Henry VII, (pp 374 of book) and a brass yard and a brass ell from 1588 in the time of Queen Elizabeth and still in use at the time, held at the
Exchequer In the Civil Service (United Kingdom), civil service of the United Kingdom, His Majesty's Exchequer, or just the Exchequer, is the accounting process of central government and the government's ''Transaction account, current account'' (i.e., mon ...
; (pp 364,365 of book) a brass yard and a brass ell at the
Guildhall A guildhall, also known as a guild hall or guild house, is a historical building originally used for tax collecting by municipalities or merchants in Europe, with many surviving today in Great Britain and the Low Countries. These buildings commo ...
; and a brass yard presented to the Clock-Makers' Company by the Exchequer in 1671. The Exchequer yard was taken as "true"; the variation was found to be + to − of an inch, and an additional graduation for the Exchequer yard was made on the Royal Society's standard. In 1758 the legislature required the construction of a standard yard, which was made from the Royal Society's standard and was deposited with the clerk of the
House of Commons The House of Commons is the name for the elected lower house of the Bicameralism, bicameral parliaments of the United Kingdom and Canada. In both of these countries, the Commons holds much more legislative power than the nominally upper house of ...
; it was divided into feet, one of the feet into inches, and one of the inches into tenths. A copy of it, but with upright cheeks between which other measuring rods could be placed, was made for the Exchequer for commercial use.


19th-century Britain

Following
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
investigations by John Playfair,
William Hyde Wollaston William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable i ...
and John Warner in 1814 a committee of parliament proposed defining the standard yard based upon the length of a
seconds pendulum A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 0.5 Hz. Principles A pendulum is a weight suspended from a pivot so tha ...
. This idea was examined but not approved. The Weights and Measures Act 1824 ( 5 Geo. 4. c. 74) ''An Act for ascertaining and establishing Uniformity of Weights and Measures'' stipulates that: In 1834, the primary Imperial yard standard was partially destroyed in a fire known as the Burning of Parliament.. In 1838, a commission was formed to reconstruct the lost standards, including the troy pound, which had also been destroyed. In 1845, a new yard standard was constructed based on two previously existing standards known as A1 and A2, both of which had been made for the Ordnance Survey, and R.S. 46, the yard of the
Royal Astronomical Society The Royal Astronomical Society (RAS) is a learned society and charitable organisation, charity that encourages and promotes the study of astronomy, planetary science, solar-system science, geophysics and closely related branches of science. Its ...
. All three had been compared to the Imperial standard before the fire. The new standard was made of Baily's metal No. 4 consisting of 16 parts copper, parts tin, and 1 part zinc. It was 38 inches long and 1 inch square. The Weights and Measures Act 1855 granted official recognition to the new standards. Between 1845 and 1855 forty yard standards were constructed, one of which was selected as the new Imperial standard. Four others, known as 'parliamentary copies', were distributed to the Royal Mint, the Royal Society of London, the Royal Observatory at Greenwich, and the New Palace at Westminster, commonly called the Houses of Parliament. The other 35 yard standards were distributed to the cities of London, Edinburgh, and Dublin, as well as the United States and other countries (although only the first five had official status). The imperial standard received by the United States is known as "Bronze Yard No. 11" The Weights and Measures Act 1878 ( 41 & 42 Vict. c. 49) confirmed the status of the existing yard standard, mandated regular intercomparisons between the several yard standards, and authorized the construction of one additional Parliamentary Copy (made in 1879 and known as Parliamentary Copy VI).


Definition of the yard in terms of the meter

Subsequent measurements revealed that the yard standard and its copies were shrinking at the rate of one part per million every twenty years due to the gradual release of strain incurred during the fabrication process. The international prototype meter, on the other hand, was comparatively stable. A measurement made in 1895 determined the length of the meter at inches relative to the imperial standard yard. The Weights and Measures (Metric System) Act 1897 ( 60 & 61 Vict. c. 46) in conjunction with Order in Council 411 (1898) made this relationship official. After 1898, the ''de facto'' legal definition of the yard came to be accepted as of a meter. The yard (known as the "international yard" in the United States) was legally defined to be exactly 0.9144
meter The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...
in 1959 under an agreement in 1959 between Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States.A. V. Astin & H. Arnold Karo, (1959)
''Refinement of values for the yard and the pound''
Washington DC:
National Bureau of Standards The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sc ...
, republished on
National Geodetic Survey The National Geodetic Survey (NGS) is a List of federal agencies in the United States, United States federal agency based in Washington, D.C. that defines and manages a national geographic coordinate system, coordinate system, providing the fou ...
web site and the
Federal Register The ''Federal Register'' (FR or sometimes Fed. Reg.) is the government gazette, official journal of the federal government of the United States that contains government agency rules, proposed rules, and public notices. It is published every wee ...
(Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)
In the UK, the provisions of the treaty were ratified by the Weights and Measures Act 1963. The Imperial Standard Yard of 1855 was renamed the United Kingdom Primary Standard Yard and retained its official status as the national prototype yard.


Current use

The yard is used to define the dimensions of the playing area in
American football American football, referred to simply as football in the United States and Canada and also known as gridiron football, is a team sport played by two teams of eleven players on a rectangular American football field, field with goalposts at e ...
,
Canadian football Canadian football, or simply football, is a Sports in Canada, sport in Canada in which two teams of 12 players each compete on a field long and wide, attempting to advance a Ball (gridiron football), pointed oval-shaped ball into the opposi ...
,
association football Association football, more commonly known as football or soccer, is a team sport played between two teams of 11 Football player, players who almost exclusively use their feet to propel a Ball (association football), ball around a rectangular f ...
,
cricket Cricket is a Bat-and-ball games, bat-and-ball game played between two Sports team, teams of eleven players on a cricket field, field, at the centre of which is a cricket pitch, pitch with a wicket at each end, each comprising two Bail (cr ...
, and in some countries
golf Golf is a club-and-ball sport in which players use various Golf club, clubs to hit a Golf ball, ball into a series of holes on a golf course, course in as few strokes as possible. Golf, unlike most ball games, cannot and does not use a standa ...
. There are corresponding units of
area Area is the measure of a region's size on a surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an open surface or the boundary of a three-di ...
and
volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...
, the
square yard The square yard (Indian English, Northern India: guz, gaj, Pakistani English, Pakistan: gaz) is an imperial unit and U.S. customary unit of area. It is in widespread use in most of the English language, English-speaking world, particularly the U ...
and
cubic yard A cubic yard (symbol yd3)IEEE Std 260.1-2004 is an Imperial unit, imperial / U.S. customary unit, U.S. customary (non-SI non-Metric system, metric) unit of volume used in Canada and the United States. It is defined as the volume of a cube with sid ...
respectively. These are sometimes referred to simply as "yards" when no ambiguity is possible, for example an American or Canadian concrete mixer may be marked with a capacity of " 9 yards" or "1.5 yards", where cubic yards are obviously referred to. Yards are also used and are the legal requirement on
road sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduc ...
s for shorter distances in the United Kingdom, and are also frequently found in conversation between Britons much like in the United States for distance.


Textiles and fat quarters

The yard, subdivided into eighths, is used for the purchase of fabrics in the United States and United Kingdom and was previously used elsewhere. In the United States the term "fat quarter" is used for a piece of fabric which is half a yard in length cut from a roll and then cut again along the width so that it is only half the width of the roll, thus the same area as a piece of one quarter yard cut from the full width of the roll; these pieces are popular for patchwork and quilting. The term "fat eighth" is also used, for a piece of one quarter yard from half the roll width, the same area as one eighth cut from the roll.


Equivalences

For purposes of measuring cloth, the early yard was divided by the binary method into two, four, eight and sixteen parts. The two most common divisions were the fourth and sixteenth parts. The quarter of a yard (9 inches) was known as the "quarter" without further qualification, while the sixteenth of a yard (2.25 inches) was called a nail. The eighth of a yard (4.5 inches) was sometimes called a
finger A finger is a prominent digit (anatomy), digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities (i.e. hands) such as humans and other primates. Most tetrapods have five digits (dactyly, pentadact ...
, but was more commonly referred to simply as an eighth of a yard, while the half-yard (18 inches) was called "half a yard". Other units related to the yard, but not specific to cloth measurement: two yards are a
fathom A fathom is a unit of length in the imperial and the U.S. customary systems equal to , used especially for measuring the depth of water. The fathom is neither an international standard (SI) unit, nor an internationally accepted non-SI unit. H ...
and a quarter of a yard (when not referring to cloth) is a span.


Conversions

: (international) yards = survey yards = meters. : (international) yards = meters. : survey yards = meters. :1 (international) yard = survey yards = meters. :1 survey yard ≈ meters. :1 (international) statute mile = 8 international
furlong A furlong is a measure of distance in imperial units and United States customary units equal to one-eighth of a mile, equivalent to any of 660 foot (unit), feet, 220 yards, 40 rod (unit), rods, 10 chain (unit), chains, or a ...
s = 80 international chains = (international) yards. :1 survey mile = 8
furlong A furlong is a measure of distance in imperial units and United States customary units equal to one-eighth of a mile, equivalent to any of 660 foot (unit), feet, 220 yards, 40 rod (unit), rods, 10 chain (unit), chains, or a ...
s = 80 chains = survey yards. Where * ''pre-1959 US yard'' – defined 1869, implemented 1893,NIST Guide to the SI – section B.6 U.S. survey foot and mile
/ref> deprecated 2023 For survey purposes, certain pre-1959 units were retained, usually prefaced by the word "survey," among them the survey inch, survey foot, and survey mile, also known as the statute mile. The rod and
furlong A furlong is a measure of distance in imperial units and United States customary units equal to one-eighth of a mile, equivalent to any of 660 foot (unit), feet, 220 yards, 40 rod (unit), rods, 10 chain (unit), chains, or a ...
existed only in their pre-1959 form and are thus not prefaced by the word "survey", and were deprecated at the same time as the survey foot. New conversion factors for the rod and furlong as 16.5 international feet and 660 international feet respectively have been published by NIST. However, it is not clear if a "survey yard" actually existed.NIST Handbook 44 – 2012 Appendix C "General Tables of Units of Measurement" page C-5
/ref> * ''international yard'' (defined 1959):


See also

* Guz, a similar unit used in Asia * 3 ft gauge railways * Vara * Yardstick


Notes


References


Citations


Bibliography

* . * . * . * . * . * . * . * . * . * . * . * . * .  &  & * .


External links

* {{United States Customary Units Units of length Imperial units Customary units of measurement in the United States Human-based units of measurement