The hundredweight or centum weight (abbreviated cwt) is a unit of mass defined in terms of the pound (lb). The definition used in Britain differs from that used in North America. The two are distinguished by the terms long hundredweight and short hundredweight:
The long hundredweight is defined as 112 lb (8 stone), which is equal to 50.802345 kg. This is the definition used in the imperial system.
The short hundredweight is defined as 100 lb, which is equal to 45.359237 kg. This is the definition used in the US customary system. This is also the usual hundredweight in Canada. The short hundredweight is also called a cental, especially in places which normally use the long hundredweight.
Under both conventions, there are twenty hundredweight in a ton, the long ton being 2,240 lb and the short ton being 2,000 lb.
The long and short hundredweight are both descended from the French avoirdupois weight system, which became established in England in Late Medieval times. British custom came widely to use the stone weight, which is 14 pounds, and wished for the hundredweight to be a whole number of stones (100 is not a multiple of 14).
The stone was not one of the avoirdupois units in Medieval France, and never became customary in the British American colonies or the US. In 1824 in the UK, new weights and measures legislation made it illegal for merchants to use the word "hundredweight" in the sense of a hundred pounds. A merchant could be sued for fraud for doing so. In 1879, the hundred-pound weight was re-legalized for trade in the UK under the name "cental", in response to legislative pressure from UK merchants who were importing wheat and tobacco from the US.
A few decades ago, commodities weighed in terms of long hundredweight included cattle, cattle fodder, fertilizers, coal, some industrial chemicals, other industrial materials, and so on. However, since increasing metrication in most English-speaking countries, it is now less used. Church bell ringers use the unit commonly, although church bell manufacturers are increasingly moving over to the metric system.
Before the 15th century in England, a hundredweight was a different unit equal to 108 lb.