|US customary/Imperial units|
|36 in||3 ft|
A yard (abbreviation: yd) is a unit of length in the imperial and United States customary systems of measurement. Historically a yard was also used in other systems of units. The yard is equal to 3 feet or 36 inches. Under an agreement in 1959 between Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States, the yard (known as the "international yard" in the United States) was legally defined to be exactly 0.9144 metres. Prior to that date, the legal definition of the yard when expressed in terms of metric units varied slightly from country to country.
Equivalence to other units of length
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 was known as the "quarter" without further qualification, while the sixteenth of a yard was called a nail. The eighth of a yard was sometimes called a finger, but was more commonly referred to simply as an eighth of a yard, while the half-yard was called "half a yard".
The yard derives its name from the Anglo-Saxon word for a straight branch or rod. In the Middle Ages, the same word (or its variants) had meanings that included measuring rod and rod (16 1⁄2 feet). The earliest known occurrence of the word (in the sense of "rod") is in Matthew xi. 7 of the Lindisfarne Gospels.
The word "yard" is a homonym of "yard" in the sense of an enclosed area of land, a word related to the verb "to gird", This second meaning of yard has a completely different etymology from the first and is not related.
The precise origin of the measure is not definitely known. Some believe it derived from the double cubit, or that it originated from cubic measure, others from its near equivalents, such as the length of a stride or pace. One postulate was that the yard was derived from the girth of a person's waist, while another claim held that the measure was invented by Henry I of England as being the distance between the tip of his nose and the end of his thumb.
Tenth-century king Edgar the Peaceable is sometimes credited with having instituted the yard by a statute known as III Edgar 8.1, dated 959-63, from the Witenagemot at Andover. The statute, which survives in several variant manuscripts, says in effect that the measure of Winchester shall be observed throughout the realm. (A variant reading has it as Winchester and London.) The chief proponents of the Edgar theory were Henry William Chisholm (Warden of the Standards, 1867–77) and Captain George Tyrrell McCaw, CMG, OBE (editor of the Empire Survey Review).
The theory that Henry I invented the yard is based on a single line of text in William of Malmesbury's History of the Kings of England (Gesta Regum Anglorum). Translated from the original Latin, it reads: The measure of his own arm was applied to correct the false ell of the traders and enjoined on all throughout England. The part about Henry's nose was added some centuries later. Even though Watson dismisses as "childish" the suggestion that the original yard was the length of the king's arm, R. D. Connor, in The Weights and Measures of England, says that William of Malmesbury is generally a reliable informant for events taking place in his own lifetime, and that the French pied du roi supposedly derived from the foot of Charlemagne.
It was first defined in law by a document thought to date from 1266-1303 known variously as the Composition of Yards and Perches, Compositio Ulnarum et Perticarum, or The statute of ells and perches. The text from the manuscript known as BL Cotton MS Claudius D 2 (as published in Ruffhead's Statutes at Large) reads:
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.
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.
The Composition of Yards and Perches belongs to a class of documents known as Statutes of uncertain date generally thought to be from c. 1250 to 1305. Although not originally statutes, they gradually acquired the force of law. In some early statute books Composition of Yards and Perches was appended to another statute of uncertain date, the Statute for the Measuring of Land also known as Statutum de Admensuratione Terrase, An Ordinance for Measuring of Land, sometimes (erroneously) listed as 33° Edward I. st. 6. (1305). The Composition of Yards and Perches was repealed by the Weights and Measures Act of 1824 (5 George IV c. 74, par. 23).
Yard and inch
In a law of 1439 (18 Henry VI. Cap. 16.) the sale of cloth by the "yard and handful" was abolished, and the "yard and inch" instituted.
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 Edward VI Cap. 6. An Act for the true making of Woolen Cloth.)
- "XIV. And that all and every Broad Cloth and Clothes called Taunton Clothes, Bridgwaters, and other Clothes which shall be made after the said Feast in Taunton, Bridgwater or in other Places of like Sort, shall contain at the Water in Length betwixt twelve and thirteen Yards, Yard and Inch of the Rule, and in Breadth seven Quarters of a Yard: (2) And every narrow Cloth made after the said Feast in the said Towns or elsewhere of like Sorts, shall contain in the Water in Length betwixt three and twenty and five and twenty Yards, Yard and Inch as is aforesaid, and in Breadth one Yard of like Measure; (3) and every such Cloth, both Broad and Narrow being well scowred, thicked, milled and fully dried, shall weigh xxxiv. li. the Piece at the least."
- "XV. And that all Clothes named Check-Kersie and Straits, which shall be made after the said Feast shall contain being wet between seventeen and eighteen Yards, with the Inches as is aforesaid, and in Breadth one Yard at the least at the Water; and being well scowred, thicked, milled and fully dried, shall weigh xxiv. li. the Piece at the least."
And once in legislation of 1557-8 (4 & 5 Philip and Mary Cap. 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 we find the same principle mentioned once again (35 Elizabeth. Cap. 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,..."
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 5⁄8 inch in diameter and 1⁄100 inch 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. Bartholemew'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. The Exchequer yard was taken as "true"; the variation was found to be +1⁄20 to -1⁄15 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; 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.
Following Royal Society investigations by John Playfair, 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 of 1824 (5° George IV. Cap. 74.) An Act for ascertaining and establishing Uniformity of Weights and Measures stipulates that:
From and after the First Day of May One thousand eight hundred and twenty five the Straight Line or Distance between the Centres of the Two Points in the Gold Studs of the Straight Brass Rod now in the Custody of the Clerk of the House of Commons whereon the Words and Figures "Standard Yard 1760" are engraved shall be and the same is hereby declared to be the original and genuine Standard of that Measure of Length or lineal Extension called a Yard; and that the same Straight Line or Distance between the Centres of the said Two Points in the said Gold Studs in the said Brass Rod the Brass being at the Temperature of Sixty two Degrees by Fahrenheit's Thermometer shall be and is hereby denominated the Imperial Standard Yard and shall be and is hereby declared to be the Unit or only Standard Measure of Extension, wherefrom or whereby all other Measures of Extension whatsoever, whether the same be lineal, superficial or solid, shall be derived, computed and ascertained; and that all Measures of Length shall be taken in Parts or Multiples, or certain Proportions of the said Standard Yard; and that One third Part of the said Standard Yard shall be a Foot, and the Twelfth Part of such Foot shall be an Inch; and that the Pole or Perch in Length shall contain Five such Yards and a Half, the Furlong Two hundred and twenty such Yards, and the Mile One thousand seven hundred and sixty such Yards.
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. 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, 2 1⁄2 parts tin, and 1 part zinc. It was 38 inches long and 1 inch square. The Weights and Measures Act of 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 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 confirmed the status of the existing yard standard, mandated regular intercomparisons between the several yard standards, and authorised the construction of one additional Parliamentary Copy (made in 1879 and known as Parliamentary Copy VI).
Definition of the yard in terms of the metre
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 metre, on the other hand, was comparatively stable. A measurement made in 1895 determined the length of the metre at 39.370113 inches relative to the imperial standard yard. The Weights and Measures (Metric) Act of 1897 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 36⁄39.370113 of a metre.
In 1959, the USA, UK, Canada, Australia, New Zealand, and South Africa agreed to adopt the international yard of exactly 0.9144 metres. In the UK, the provisions of the treaty were ratified by the Weights and Measures Act of 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.
Schedule 2, Part I of The Weights and Measures Act of 1985 defines the yard as 0.9144 metres, and the metre as the distance light travels in 1⁄299792458 of a second. It then goes on to state:
- Description of United Kingdom primary standard of the yard A solid bronze bar, about 38 inches long and about 1 inch square in transverse section, marked “Copper 16 oz. Tin 2½ Zinc 1 Mr. Baily’s Metal No. 1 STANDARD YARD at 62°·00 Faht. Cast in 1845 Troughton & Simms, LONDON
- Part V Authorised copies of United Kingdom primary standards of the yard and pound ... (e) a bronze bar marked “Copper 16 oz. Tin 2½ inc 1. 
The yard is used as the standard unit of field-length measurement in American, Canadian and Association football, cricket pitch dimensions, and in some countries, golf fairway measurements.
There are corresponding units of area and volume: the square yard and cubic yard 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 "11 yards" or "1.5 yards", where cubic yards are obviously referred to.
- 1 yard = 0.9144 metre.
- 1 statute mile (international mile) = 8 furlongs = 80 chains = 1760 yards
- pre-1959 US yard - defined 1869, implemented 1893
- 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 exist only in their pre-1959 form and are thus not prefaced by the word "survey." However, it is not clear if a "survey yard" actually exists. If it did, its hypothetical values would be as follows:
- 3937 survey yard = 3600 metre
- 1 survey yard ≈ 0.914 401 83 metre
- 0.999 998 survey yard = 1 yard (exact)
- 1 statute mile (US survey mile) = 8 furlongs = 80 chains = 1760 survey yards (about 1.000002 international miles)
- English units
- Guz, the yard of the Middle East
- Imperial units
- Nail (unit)
- United States customary units
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