The avoirdupois (IPA: /ˌævərdəˈpɔɪz/; French IPA: [avwɑrdypwɑ]) system is a system of weights (or, properly, mass) based on a pound of sixteen ounces. It is the everyday system of weight used in the United States. It is still widely used by many people in Canada and the United Kingdom despite the official adoption of the metric system, including the compulsory introduction of metric units in shops. It is considered more modern than the alternative troy or apothecary or the medieval English mercantile and Tower systems.
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History of the term
The word avoirdupois is from French and Middle English (Anglo-French) avoir de pois, "goods of weight" or "goods sold by weight", and from Old French aveir de peis, literally "goods of weight", from aveir, "property, goods" (from aveir, "to have", from Latin habere, "to have, to hold, to possess property") + de, "from" (from the Latin) + peis, "weight", from Latin pensum, "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 imaginative 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 1600s "de" was replaced with "du".)
Original forms
These are the units in their original French forms:
| Table of mass units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
Notes | |||
| dram or drachm | 1/256 | 1/16 once | |||
| once | 1/16 | 1/16 livre | |||
| livre | 1 | ||||
| quintal | 100 | plural: quintaux | |||
| tonne | 2000 | ||||
British adaptation
When people in Britain began to use this system they included the stone, which was eventually defined as fourteen avoirdupois pounds. The quarter, hundredweight, and ton were altered, respectively, to 28 lb, 112 lb, and 2240 lb in order for masses to be easily converted between them and stone. The following are the units in the British or imperial adaptation of the avoirdupois system:
| Table of mass units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
Metric value |
Notes | ||
| dram or drachm | 1/256 | ~1.772 g | 1/16 oz | ||
| ounce (oz) | 1/16 | ~28.35 g | 1/16 lb | ||
| pound (lb) | 1 | ~453.6 g | |||
| stone (st) | 14 | ~6.35 kg | 14 lb. The plural form is conventionally written the same as the singular, 'stone'. | ||
| quarter (qtr) | 28 | ~12.7 kg | 2 st. Sometimes called the 'long quarter' to distinguish it from the U.S. unit. | ||
| hundredweight (cwt) | 112 | ~50.8 kg | 4 qtr. Sometimes called the 'long hundredweight' to distinguish it from the 'short hundredweight'. | ||
| ton (t) | 2240 | ~1016 kg | 20 cwt. Sometimes called the 'long ton' to distinguish it from the short ton. | ||
American customary system
The Thirteen British colonies in North America (not including those that formed Canada), however, adopted the French system as it was. In the U.S., quarters, hundredweights, and tons remain defined as 25, 100, and 2000 lb (though the quarter is virtually unused, as is the hundredweight outside of agriculture and commodities); if disambiguation is required then tons are referred to as the "short" units, as opposed to the British "long" units.
| Table of mass units | |||||
|---|---|---|---|---|---|
| Unit | Relative value |
Metric value |
Notes | ||
| dram (dr) | 1/256 | ~1.772 g | 1/16 oz | ||
| ounce (oz) | 1/16 | ~28.35 g | 1/16 lb | ||
| pound (lb) | 1 | ~453.6 g | |||
| quarter (qtr) | 25 | ~11.34 kg | 25 lb. Not used to any significant extent. | ||
| hundredweight (cwt) | 100 | ~45.36 kg | 4 qtr. Sometimes called the 'short hundredweight' to distinguish it from the long hundredweight. | ||
| ton (t) | 2000 | ~907.2 kg | 20 cwt. Sometimes called the 'short ton' to distinguish it from the long ton. | ||
Internationalization
In the avoirdupois system, all units are multiples or fractions of the pound, which is now defined as 0.45359237 kg 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.
See also
- French units of measurement
- Apothecaries' system of mass
- Imperial unit
- Troy weight
- U.S. customary units
References
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| Metric systems | International System of Units · centimetre-gram-second units · metre-tonne-second units · gravitational units |
| Natural units | Geometric unit systems · Planck units · Stoney units · "Schrödinger" units · Atomic units · Electronic units · Quantum electrodynamical units |
| Customary systems | Avoirdupois units · Troy units · Apothecaries' units · English units · Imperial units · Canadian units · US customary units · Danish units · Dutch units · Finnish units · French units · German units · Maltese units · Metric system · Norwegian units · Scottish units · Spanish/Portuguese units · Swedish units · Polish units · Romanian units · Russian units · Tatar units · Hindu units · Pegu units · Chinese units · Japanese units · Taiwanese units |
| Ancient systems | Greek units · Roman units · Egyptian units · Hebrew units · Arabic units · Mesopotamian units · Persian units · Harappan units |
| Other systems | Non-standard measurement units · Mesures usuelles |
