Ton

Ton is any of several units of measure of mass, volume or force. It has a long history and has acquired several meanings and uses.
As a unit of mass, ton can mean:

the long ton, which is
the tonne, also called the metric ton, which is ) or 1 megagram.
the short ton, which is

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 is usually the heaviest unit named in colloquial 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."

History

The ton is derived from the tun, the term applied to a cask of the largest capacity. This could contain a volume between, which could weigh around, and occupy some of cargo space.

Units of mass/weight

There are several similar units of mass or volume called the ton:

Full name	Common name	Quantity	Symbol	Notes
long ton	"ton"		LT	Used in Ireland and Commonwealth countries that formerly used, or still use the Imperial system
short ton	"ton"		tn or st	Used in the United States and in some industries in Canada
tonne	"tonne"; "metric ton"	1,000 kg	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		Used in the iron industry in the 17th and 18th centuries.

The difference between the short ton and the other common forms 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.

Other units of mass/weight

Deadweight ton is a measure of a ship's carrying capacity, including bunker oil, fresh water, ballast water, crew, and provisions. It is expressed in tonnes or long tons. This measurement is also used in the U.S. tonnage of naval ships.
Increasingly, tonnes are being used rather than long tons in measuring the displacement of ships.
Harbour ton, used in South Africa in the 20th century, was equivalent to or 1 short ton.

Assay ton is not a unit of measurement but a standard quantity used in assaying 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.

Subdivisions

Both the UK definition of long ton and US definition of short ton have similar underlying bases. Each is equivalent to 20 hundredweight; however, they are long and short hundredweight, respectively.
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.
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.

Units of volume

The displacement, essentially the weight, of a ship is traditionally expressed in long tons. To simplify measurement it is determined by measuring the volume, rather than weight, of water displaced, and calculating the weight from the volume and density.
For practical purposes the displacement ton is a unit of volume,, the approximate volume occupied by one ton of seawater. It is slightly less than the 224 imperial gallons of the water ton.
One measurement 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 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.
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 gallon.

Colloquial English

Ton is also used informally, often as slang, to mean a large amount of something.
In Britain, a ton is colloquially used to refer to 100 of a given unit. Ton can thus refer to a speed of 100 miles per hour, and is prefixed by an indefinite article, e.g. "Lee was doing a ton down the motorway"; to money e.g. "How much did you pay for that?" "A ton" ; to 100 points in a game e.g. "Eric just threw a ton in our darts game" ; or to a hundred of any other countable figure.