The avoirdupois system is a system of weights
based on a pound of 16 ounces. It is the everyday system of weight used in the United States
and is still used to varying degrees in everyday life in the United Kingdom, Canada, and some
other former British colonies despite the official adoption of the metric system. An
alternative system of mass, the Troy system, is generally used for precious materials.
The modern definition of the avoirdupois pound is exactly 0.45359237 kilograms. Etymology
The word avoirdupois is from Anglo-Norman French aveir de peis, literally “goods of
weight”. This term originally referred to a class of merchandise: aveir de peis, “goods
of weight”, things that were sold in bulk and were weighed on large steelyards or balances.
Only later did it become identified with a particular system of units used to weigh such
merchandise. The orthography of the day has left many variants of the term, such as haberty-poie
and haber de peyse. History There are two major hypotheses regarding the
origins of the avoirdupois system. The older hypothesis is that it originated in France.
A newer hypothesis is that it is based on the weight system of Florence.
The avoirdupois weight system is thought to have come into use in England circa 1300.
It was originally used for weighing wool. In the early 14th century several other specialized
weight systems were used, including the weight system of the Hanseatic League with a 16-ounce
pound of 7200 grains and an 8-ounce mark. However, the main weight system, used for
coinage and for everyday use, was based on the 12-ounce Tower pound of 5400 grains. From
the 14th century until late 16th century, the avoirdupois pound was also known as the
wool pound or the avoirdupois wool pound. The earliest known version of the avoirdupois
weight system had the following units: a pound of 6992 grains, a stone of 14 pounds, a woolsack
of 26 stone, an ounce of 1/16 pound, and finally, the ounce was divided into 16 “parts.”
The earliest known occurrence of the word “avoirdupois” in England is from a document
entitled Tractatus de Ponderibus et Mensuris or Treatise on Weights and Measures. This
document is listed in early statute books under the heading 31 Edward I dated 2 February
1303. More recent statute books list it under Statutes of uncertain date. Scholars nowadays
believe that it was probably written between 1266 and 1303. Initially a royal memorandum,
it eventually took on the force of law and was recognized as a statute by King Henry
VIII and Queen Elizabeth I. It was repealed by the Weights and Measures Act of 1824. In
the Tractatus, the word “avoirdupois” refers not a weight system, but to a class of goods,
specifically, heavy goods sold by weight, as opposed to goods sold by volume, by count,
or by some other method. Since it is written in Anglo-Norman French, it is not accounted
the first occurrence of the word in the English language
Three major developments occurred during the reign of Edward III. First, a statute known
as 14o Edward III. st. 1. Cap. 12 “Bushels and Weights shall be made and sent into every
Country.” Original: “& acorde qe desore en avant un
mesure & un pois soit parmy toute Engleterre & qe le Tresorer face faire certaines estandardz
de bussel de galon de poys darreisne & les face mander en chescune countee par la ou
tielx estandardz ne sont pas avant ces hures mandez”
English translation: “(4) it is assented and accorded,That from henceforth one Measure
and one Weight shall be throughout the Realm of England; and that the Treasurer cause to
be made certain Standards of Bushels Gallons of Weights of Auncel, and send the same into
every County where such Standards be not sent before this Time;”
The second major development is the statute 25o Edward III. st. 5. Cap. 9. “The Auncel
Weight shall be put out, and Weighing shall be by equal Balance.”
Original: “qe le sak de leine ne poise qe vint & sys peres & chescun pere poise quatorze
livres” English translation: “so that the Sack of
Wooll weigh no more but xxvi. Stones, and every Stone to weigh xiv. l.”
The third development is a set of 14th-century bronze weights at the Westgate Museum in Winchester,
England. The weights are in denominations of 7 pounds, 14 pounds, 56 pounds and 91 pounds.
The 91-pound weight is thought to have been commissioned by Edward III in conjunction
with the statute of 1350, while the other weights are thought to have been commissioned
in conjunction with the statutes of 1340. The 56-pound weight was used as a reference
standard as late as 1588. A statute of Henry VIII made avoirdupois weights
mandatory. In 1588 Queen Elizabeth increased the weight
of the avoirdupois pound to 7000 grains and added the troy grain to the avoirdupois weight
system. Prior to 1588, the “part” was the smallest unit in the avoirdupois weight system.
In the 18th century, the “part” was renamed “drachm.”
Original forms These are the units in their original Anglo-Norman
French forms: Post-Elizabethan
In the United Kingdom, 14 avoirdupois pounds equals one stone. The quarter, hundredweight,
and ton equal respectively, 28 lb, 112 lb, and 2,240 lb in order for masses to be easily
converted between them and stones. The following are the units in the British or imperial version
of the avoirdupois system: Note: The plural form of the unit stone is
either stone or stones, but stone is most frequently used.
American customary system The 13 British colonies in North America used
the avoirdupois system. But they continued to use the British system as it was, without
the evolution that was occurring in Britain in the use of the stone unit. In 1824 there
was landmark new weights and measures legislation in the United Kingdom that the United States
did not adopt. In the United States, quarters, hundredweights,
and tons remain defined as 25, 100, and 2,000 lb respectively. The quarter is now virtually
unused, as is the hundredweight outside of agriculture and commodities. If disambiguation
is required, then they are referred to as the smaller “short” units in the United States,
as opposed to the larger British “long” units. Grains are used worldwide for measuring gunpowder
and smokeless powder charges. Historically, the dram has also been used worldwide for
measuring gunpowder charges, for measuring powder charges for shotguns and large black-powder
rifles. Internationalization
In the avoirdupois system, all units are multiples or fractions of the pound, which is now defined
as 0.453 592 37 kg exactly in most of the English-speaking world since the implementation
of the international yard and pound agreement of 1959.
Due to the ambiguous meanings of “weight” as referring to both mass and force, it is
sometimes erroneously asserted that the pound is only a unit of force. However, as defined
above the pound is a unit of mass, which agrees with common usage. Also see pound-force, poundal
and pound-mass. See also
Apothecaries’ system Units of measurement in France
Imperial units Troy weight
United States customary units References External links
A bronze Edward III standard weight of 14lb A bronze Edward III standard weight of 91lb

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