In the Imperial units, a hundred weight is defined as 112 pounds avoirdupois, i.e. 8 stoness or four quarterss. This equals 50.802Kg, and many commodities that were previously packed or sold by the hundredweight are now packed or sold in 50Kg units instead.

In the U.S. customary units, a hundredweight is defined as 100 pounds. This equals 45.359Kg. This unit was introduced in the late 1800s.

In both systems, there are twenty hundredweights to a ton - in Imperial units this is the long ton of 2240 pounds (approximately equal to a metric tonne), and in US units it is 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). The US unit is commonly used in shipping and in the exchange of futures. The Imperial unit is now little used since it is not on a scale that has much household use, and for all technical purposes metric units are now in use in both the UK and Ireland, while other Commonwealth countries have adopted the metric system in full.