Hundred weight or hundredweight is a unit of measurement for mass in both the system of measurement used in the United Kingdom and Ireland (and previously throughout the British Commonwealth), and in the system used in the United States. However, its definition differs in the two systems.
- In Imperial units, a hundredweight was defined as 112 pounds avoirdupois, or 8 stones, or four quarters . This is so close to 50 kg that the transition to metric equivalents has been easy. It has now been legally defined in Britain as 50.80234544 kg.
- In U.S. customary units, a hundredweight is defined as 100 pounds. The short hundredweight is also the normal hundredweight in Canada.
- The short hundredweight is also called a cental (which never means a long hundredweight), especially in places which normally use the long hundredweight. See Conversion of units#Mass
In both systems, there are twenty hundredweights to a ton – the long ton of 2240 pounds (approximately equal to a metric tonne), and the short ton of 2000 pounds. In both systems, the hundredweight is abbreviated cwt, where wt is an abbreviation for weight and c is an abbreviation for one hundred (since the Roman numeral C is equal to 100).
Prior to the 15th century in England, a hundredweight used the old hundred of 108 lb, giving a ton of 2160 pounds. In some industries (notably forges) this old hundred was retained somewhat longer. The London hundredweight of 112 pounds eventually replaced the old hundred.
The short hundredweight is commonly used in the sale of livestock and some grains and oilseeds and in the exchange of futures. The long hundredweight is now little used in any country. In the UK and Ireland, the few household commodities that were commonly sold by the hundredweight, such as coal and some building materials, are now sold in 50 kg quantities. For most purposes metric units are now in use in both the UK and Ireland, while other Commonwealth countries have adopted the metric system in full.
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