Ton

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For ton as a unit of volume see Ton (volume)

There are three similar units of mass called the ton or tonne:

tonne (SI) or metric ton = 1000 kg (2204 lb). The official symbol is t, but mT and T are also used.
short ton (or simply ton in casual use in the USA) = 907.185 kg (2000 lb).
long ton (or weight ton) = 1016.047 kg (2240 lb), was commonly used in the UK (before it adopted the 1000 kg tonne) and for petroleum products.

Both the short ton and the long ton are composed of twenty hundredweights, each having different values for the hundredweight (100 and 112 pounds respectively). Prior to the 15th century in England, the ton was still composed of twenty hundredweights, but each was 108 lbs, giving a ton of 2160 pounds.

The word ton or tonne is derived from the Old English tunne, and ultimately from the Old French tonne, and referred originally to a large cask with a capacity of 252 gallons, which holds approximately 2016 pounds of water. Such a barrel is still called a tun in British English, but this usage is dying out.

Ton is also used informally to mean a large amount of something.