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Ton is any of several units of measure of mass, volume or Ton-force. It has a long history and has acquired several meanings and uses.
As a unit of mass, ton can mean:
Its original use as a unit of volume has continued in the capacity of cargo ships and in units such as the freight ton and a number of other units, ranging from in size.
Because the ton (of any system of measuring weight) is usually the heaviest unit named in colloquialism speech, its name also has figurative uses, singular and plural, informally meaning a large amount or quantity, or to a great degree, as in "There's a ton of bees in this hive," "We have tons of homework," and "I love you a ton."
| long ton | "ton" (United Kingdom) | LT | Used in Ireland and Commonwealth countries that formerly used, or still use the Imperial unit | |
| short ton | "ton" (United States) | tn or st | Used in the United States and in some industries in Canada | |
| tonne (equivalent to one megagram) | "tonne"; "metric ton" | 1,000 kg (about 2,204.6226 lb) | t | Defined in the International System of Units. Used worldwide. |
| shortweight ton | 2,240 lb | Used in the iron industry in the 17th and 18th centuries. | ||
| longweight ton | 2,400 lb |
The difference between the short ton and the other common forms ("long" and "metric") is about 10%, while the metric and long tons differ by less than 2%.
The metric tonne is usually distinguished by its spelling when written, but in the United States and United Kingdom, it is pronounced the same as ton, hence is often spoken as "metric ton" when it is necessary to make the distinction. In the United Kingdom the final "e" of "tonne" can also be pronounced (). In Australia, it is pronounced .
In Ireland and most members of the Commonwealth of Nations, a ton is defined as .
In the United States and Canada, a ton is defined as .
Assay ton (abbreviation 'AT') is not a unit of measurement but a standard quantity used in ores of precious metals. A short assay ton is approximately and a long assay ton is approximately . These amounts bear the same ratio to a milligram as a short or long ton bears to a troy ounce. Therefore, the number of milligrams of a particular metal found in a sample weighing one assay ton gives the number of troy ounces of metal contained in a ton of ore.
In documents that predate 1960 the word ton is sometimes spelled tonne, but in more recent documents tonne refers exclusively to the metric ton.
In nuclear power plants tHM and MTHM mean tonnes of heavy metals, and MTU means tonnes of uranium. In the steel industry, the abbreviation THM means 'tons/tonnes hot metal', which refers to the amount of liquid iron or steel that is produced, particularly in the context of blast furnace production or specific consumption.
Before the 20th century there were several definitions. Prior to the 15th century in England, the ton was 20 hundredweight, each of 108 lb, giving a ton of . In the 19th century in different parts of Britain, definitions of 2,240, or 2,352, or 2,400 lb were used, with 2,000 lb for explosives; the legal ton was usually 2,240 lb.Definitions of 2,000, 2,240, 2,352, and 2,400 lb are included in citations listed in the Oxford English Dictionary, 2nd ed. OED cites an 1858 dictionary of trade products "the legal ton by weight is usually 20 cwt".
In the United Kingdom, Canada, Australia, and other areas that had used the imperial system, the tonne is the form of ton legal in trade.
One Shipping ton or freight ton is equal to , but historically it has had several different definitions. It is used to determine the amount of money to be charged in loading, unloading, or carrying different sorts of cargo. In general if a cargo is heavier than salt water, the actual weight is used. If it is lighter than salt water, e.g. feathers, freight is calculated in measurement tons of 40 cubic feet.
Gross tonnage and net tonnage are volumetric measures of the cargo-carrying capacity of a ship.
The Panama Canal/Universal Measurement System (PC/UMS) is based on net tonnage, modified for Panama Canal billing purposes. PC/UMS is based on a mathematical formula to calculate a vessel's total volume; a PC/UMS net ton is equivalent to 100 cubic feet of capacity. Panama Canal Tolls , Panama Canal Authority. Retrieved 10 May 2006.
The water ton is used chiefly in Great Britain, in statistics dealing with petroleum products, and is defined as , the volume occupied by of water under the conditions that define the imperial units gallon.
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