thumb|The informal public [[imperial units|imperial measurement standards erected at the Royal Observatory, Greenwich, in the 19th century: 1 British yard, 2 feet, 1 foot, 6 inches, and 3 inches. The inexact monument was designed to permit rods of the correct measure to fit snugly into its pins at an ambient temperature of 62 °F (16.66 °C).]]
thumb|Bronze Yard No.11, the official standard of length for the [[United States between 1855 and 1892, when the Treasury Department formally adopted a metric standard. Bronze Yard No.11 was forged to be an exact copy of the British Imperial Standard Yard held by Parliament. Both are line standards: the yard was defined by the distance at 62°F between two fine lines drawn on gold plugs (closeup, top) installed in recesses near each end of the bar.]]
The yard (symbol: yd) is an English unit of length in both the British imperial and US customary systems of measurement equalling 3 feet or 36 inches. Since 1959 it has been by international agreement standardized as exactly 0.9144 meter. A distance of 1,760 yards is equal to 1 mile.
The theoretical US survey yard is very slightly longer.
Name
The term, yard derives from the Old English , etc., which was used for branches, staves and measuring rods. It is first attested in the late 7th century laws of Ine of Wessex, wherein the "yard of land" mentioned is the yardland, an old English unit of tax assessment<!--not area--> equal to hide. Old and Middle English both used their forms of "yard" to denote the surveying lengths of or , used in computing acres, 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. The usage seems to derive from the prototype standard rods held by the king and his magistrates (see below).
The word 'yard' is a homonym of 'yard' in the sense of an enclosed area of land. This second meaning of 'yard' has an etymology related to the word 'garden' and is not related to the unit of measurement.
In India 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, but Roman feet was a "step" () and 3 Welsh feet was a "pace" (). The Proto-Germanic "cubit" or arm's-length has been reconstructed as *alinô, which developed into the Old English , Middle English , 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. 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 directed the Witenagemot at Andover that "the measure held at Winchester" should be observed throughout his realm. (Some manuscripts read "at London and at Winchester".) The statutes of William I similarly refer to and uphold the standard measures of his predecessors without naming them.
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William of Malmesbury'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, 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:
<blockquote>It is ordained that 3 grains of barley dry and round do make an inch, 12 inches make 1 foot, 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.</blockquote>
The Liber Horn compilation (1311) includes that statute with slightly different wording and adds:
<blockquote>And be it remembered that the iron yard of our Lord the King containeth 3 feet and no more, and a foot ought to contain 12 inches 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.</blockquote>
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).
<blockquote>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.</blockquote>
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.)
<blockquote>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:...</blockquote>
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.)
<blockquote>(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,...</blockquote>
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, 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; a brass yard and a brass ell at the Guildhall; and a brass yard presented to the Clock-Makers' Company by the Exchequer in 1671.
19th-century Britain
Following Royal Society investigations by John Playfair, William Hyde Wollaston and John Warner in 1814 a committee of parliament proposed defining the standard yard based upon the length of a seconds pendulum. 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