The avoirdupois ( /ˌævərdəˈpɔɪz/; French pronunciation: [avwaʁdypwɑ]) system is a system of weights (or, properly, mass) based on a pound of 16 ounces. It is the everyday system of weight used in the United States and is still widely used to varying degrees by many people in Canada, the United Kingdom, and some other former British colonies despite the official adoption (or partial adoption in the case of the UK) of the metric system. An alternative system of mass is generally used for precious materials, Troy weight.
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The word avoirdupois is from Anglo-Norman French aveir de peis (later avoir de pois), literally "goods of weight" (Old French aveir, "property, goods", also "to have", comes from the Latin habere, "to have, to hold, to possess property"; de = "from"/"of", cf. Latin; peis = "weight", from Latin pensum).[1][2] 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 and the passage of the term through a series of languages (Latin, Anglo-French and English) has left many variants of the term, such as haberty-poie and haber de peyse. (The Norman peis became the Parisian pois. In the 17th century de was replaced with du.)
The earliest known occurrence of the word "avoirdupois" (or some variant thereof) 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 Ancient Statutes of Uncertain Date. Scholars nowadays believe that it was probably written between 1266 and 1303.[3] Even though it was initially a memorandum, over the years it took on the force of law, and was recognized as a statute by King Henry VIII and Queen Elizabeth I. It was repealed by the Weights and Measures Act of 1824.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 Tractutus, 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[4][5]
There are two major theories regarding the origins of the avoirdupois system. The older theory is that it originated in France.[6] A newer theory is that it is based on the weight system of Florence.[7]
Three major developments occurred during the reign of Edward III (r. 1327-77). First, a statute known as 14° Edward III. st. 1. Cap. 12 (1340) "Bushels and Weights shall be made and sent into every Country."[8]
The second major development is the statute 25° Edward III. st. 5. Cap. 9. (1350) "The Auncel Weight shall be put out, and Weighing shall be by equal Balance."[9]
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 (corresponding to a unit known as the clip or wool-clip, 14 pounds (stone), 56 ponds (4 stone) and 91 pound (1/4 sack or woolsack).[10][11] 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 commission in conjunction with the statutes of 1340.
These are the units in their original Anglo-Norman French forms:[9]
| Unit | Relative value |
Notes |
|---|---|---|
| dram or drachm | 1⁄256 | 1⁄16 once |
| once | 1⁄16 | |
| livre | 1 | |
| pere | 14 | |
| sak de leine | 364 | 26 peres |
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 adaptation of the avoirdupois system:
| Unit | Relative value |
Metric value |
Notes |
|---|---|---|---|
| dram or drachm (dr) | 1⁄256 | ≈ 1.772 g | 1⁄16 oz |
| ounce (oz) | 1⁄16 | ≈ 28.35 g | 16 dr |
| pound (lb) | 1 | ≈ 453.6 g | 16 oz |
| stone (st) | 14 | ≈ 6.350 kg | 1⁄2 qtr |
| quarter (qtr) | 28 | ≈ 12.70 kg | 2 st |
| hundredweight (cwt) | 112 | ≈ 50.80 kg | 4 qtr |
| ton (t) or long ton (l. tn.) |
2,240 | ≈ 1,016 kg | 20 cwt |
Note: The plural form of the unit stone is either stone or stones, but stone is most frequently used.
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 blackpowder rifles.
| Unit | Relative value |
Metric value |
Notes |
|---|---|---|---|
| grain (gr) | 1⁄7000 | ≈ 64.80 mg | 1⁄7000 lb |
| dram (dr) | 1⁄256 | ≈ 1.772 g | 1⁄16 oz |
| ounce (oz) | 1⁄16 | ≈ 28.35 g | 16 dr |
| pound (lb) | 1 | ≈ 453.6 g | 16 oz |
| quarter (qtr) | 25 | ≈ 11.34 kg | 25 lb |
| hundredweight (cwt) | 100 | ≈ 45.36 kg | 4 qtr |
| ton (t) or short ton (sh. tn.) |
2,000 | ≈ 907.2 kg | 20 cwt |
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 1959. (See the Mendenhall Order for references.)
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 and pound-mass.
A bronze Edward III standard weight of 14lb (1327-1377)
A bronze Edward III standard weight of 91lb (1/4 sack) (1327-1377)
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