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.
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.
Older blacksmiths' anvils are often stamped with a three-digit number indicating their total weight in hundredweight, quarter-hundredweight, and pounds. Thus, an anvil stamped "1.1.8" will weigh 148 lbs (112 lbs + 28 lbs + 8 lbs).
Before the 15th century in England, a hundredweight was a different unit equal to 108 lb.
- Text of the UK Units of Measurement Regulations 1995 as originally enacted or made within the United Kingdom, from the UK Statute Law Database , which reiterates for hundredweight the Text of the Weights and Measures Act 1985 as in force today (including any amendments) within the United Kingdom, from the UK Statute Law Database .
- NIST Guide to the SI
- Chapter VII of the book Men and measures: a history of weights and measures, ancient and modern, by Edward Nicholson (published 1912). Downloadable at Archive.org.
- William J. Murphy. "Tables for Weights and Measurement: Crops". University of Missouri Extension. http://extension.missouri.edu/xplor/agguides/crops/g04020.htm
- "Rough Rice Futures - Contract specifications". Agricultural products. CME Group. Retrieved 21 December 2010.
- "Scope, Conventions, Abbreviations, etc". Doves Guide for Church Bell Ringers. Retrieved 21 December 2010.
- "Turret Bells". Whitechapel Bell Foundry Limited. Retrieved 21 December 2010.
- "Anvils-6: Marked Weight of Anvils". Getting Started in Blacksmithing. Retrieved 15 December 2014.
- E.g., with a date a little before 1300, the "Tractatus de Ponderibus et Mensuris". Statutes of the Realm. Retrieved 3 September 2009.