Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of mass. Its original use as a measurement of volume has continued in the capacity of cargo ships and in terms such as the freight ton. It can also be used as a measure of energy, for truck classification, or as a colloquial term.
It is derived from the tun, the term applied to a barrel of the largest size. This could contain a volume between 175 and 213 imperial gallons (210 and 256 US gal), which could weigh around 2,000 pounds (910 kg) and occupy some 60 cubic feet (1.7 m3) of space.
In the United Kingdom the ton is defined as 2,240 pounds (1,016 kg) (avoirdupois pounds). From 1965 the UK embarked upon a programme of metrication and gradually introduced metric units, including the tonne (metric ton), defined as 1000 kg (2,204.6 lbs). The UK Weights and Measures Act 1985 explicitly excluded from use for trade many units and terms, including the ton and the term "metric ton" for "tonne".
