So the other day a student asked me, "How much is a ton?" Great, and she was expecting a quick and easy answer like 1000 kg. The problem is that this word has many meanings.

In the late 14th century the tonne was a unit for measuring the capacity of a ship to carry cargo. It meant the space occupied by a tun, which was a large barrel of wine. Today this tun can mean 35, 40, 42 or 100 cubic feet. A tun is not an exact measure, but is the old English word for a "large barrel", originally spelled tunne.

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A ton is 1016.0 kg (UK and Canada) or 907.2 kg (US and Canada). Sometimes these are called a long ton and a short ton. They are also called the gross ton and the net ton. A metric ton (also spelled tonne) is 1000 kg. Just to make it even more confusing the word ton is often used colloquially to mean any relatively heavy weight or large amount, for example, "My school bag weighs a ton."

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Ton or tonnage is also a measure of how much a ship or truck can carry. So a half-ton truck can carry half a ton, not that it weighs half a ton.

A ton is also a measure of cooling for freezers, refrigerators and air-conditioners. In American English a standard ton is 12,000 or sometimes 13,440 British Thermal Units an hour. In theory it is the energy needed to freeze one ton of water, depending on which ton you are measuring. In British English the metric unit kilowatt is more likely to be used instead of British Thermal Units.

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Furthermore, tons are used as the measure of the power available in natural gas as equivalent to so many tons of oil. They also measure explosive force by comparison to tons of TNT. It is also a measure of force (9806 kg m/s2 or Newtons). A volume of liquid, such as oil, equivalent to 224 British gallons is called a water ton. There is also the harbour ton at 2000 pounds. A very different measurement is the assay ton at 29.1667 grams and is used in the US to measure gold. Then there is the timber ton at 40 cubic feet and the wheat ton of 20 U.S. bushels.

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That is a lot of meanings and is very confusing to use. There is an easy solution to the problems with the word ton. Don't use it to measure anything. Always ask for the weight of something you are buying in a measurement you know. There is only one weight for the kilogram or specify "metric tons". You can still complain that you got a ton of homework, even if it is only 5 pages (29.1667 grams).

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by John Larrysson

[email protected]

A native English speaker who has been teaching practical English in Hong Kong for more than a decade.