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 weight, and as a unit of volume. 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 210 and 256 gallons, which could weigh around two thousand pounds and occupy some sixty cubic foot of space. [1]
In the United Kingdom, the ton is a unit of measure which, when it ceased to be legal for trade in 1985, was defined in British legislation as being a weight or mass equal to 2,240 pounds (1,016 kg) (avoirdupois pounds).[2] In the United States and Canada,[3] however, a ton is defined to be 2,000 pounds (907 kg). To avoid confusion, the former is more specifically referred to as a "long ton" and the latter, a "short ton"; neither should be confused with the metric ton (tonne), which is 1,000 kilograms (2,205 lb). While they do vary, a ton is generally one of the heaviest units of weight or mass referred to in colloquial speech.
The term "ton" is also used to refer to a number of units of volume, ranging from 40 to 100 cu ft in capacity.
It can also be used as a unit of energy, expressed as an equivlent of coal burnt, or TNT detonated.
Contents |
There are several similar units of mass or volume called the ton:
| Full name | Common name | Quantity | Notes |
|---|---|---|---|
| long ton, weight ton, gross ton | "ton" (UK) | 2240 pounds (1016.0469088 kg) | Used in countries such as United Kingdom that formerly used the Imperial system |
| short ton,net ton | "ton" (US) | 2000 lb | Used in North America |
| metric ton,tonne | "metric ton" | 1000 kg | In the UK and areas that used to use the Imperial system, the metric ton is the form of ton legal in trade. Conveniently it is less than 2% different from the long ton. |
| ton shortweight | 1000 lb | Used in the iron industry in the 17th century and 18th centuries. | |
| ton longweight | 2400 lb | Used in the iron industry in the 17th century and 18th centuries. |
Both the long ton and the short ton are composed of 20 hundredweight, being 112 and 100 pounds respectively. Prior to the 15th century in England, the ton was composed of 20 hundredweight, each of 108 lb, giving a ton of 2000 pounds.
Assay ton (abbreviation 'AT') is not a unit of measurement, but a standard quantity used in assaying ores of precious metals; it is 29 1⁄6 grams (short assay ton) or 32 2⁄3 grams (long assay ton), the amount which bears the same ratio to a milligram as a short or long ton bears to a troy ounce. In other words, the number of milligrams of a particular metal found in a sample of this size gives the number of troy ounces contained in a short or long 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.
A dry ton or dry tonne has the same mass value, but the material (sludge, slurries, compost, and similar mixtures in which solid material is soaked with or suspended in water) has been dried to a relatively low, consistent moisture level (dry weight). If the material is in its natural, wet state, it is called a wet ton or wet tonne.
The displacement ton is a unit of volume used for calculating the displacement of a ship.[4] While displacement is a measure of a ships weight, being the volume of water displaced multiplied by its density and measured in long tons (tons displacement), the displacement ton is the standard volume of water representing one ton displacement.[5] It equates to 35 cu ft of sea water at average density, being slightly less than the 224 imperial gallons (2240 lb), of the water ton (qv). It is usually abbreviated as DT.
One measurement ton or freight ton is equal to 40 cubic feet. It is sometimes abbreviated as "MTON".[6][7][8][9] The freight ton represents the volume of a truck, train or other freight carrier. In the past it has been used for a cargo ship but the register ton is now preferred. It is equal to 40 cubic feet (1.13 m3) of space, but historically it has had several informal definitions. It is correctly abbreviated as "FT" but some users are now using freight ton to represent a weight of 1 tonne, thus the more common abbreviations are now M/T, MT, or MTON (for measurement ton), which still cause it to be confused with the tonne, or even the megaton.
The register ton is a unit of volume used for the cargo capacity of a ship, defined as 100 cubic feet (2.83 m3). It is often abbreviated RT or GRT for gross registered ton (The former providing confusion with the refrigeration ton). It is known as a tonneau de mer in Belgium, but, in France, a tonneau de mer is 1.44 cubic metres or 1.88 cu yd.
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 (2.83 m3) of capacity.[10]
The water ton was formerly used in Great Britain and is equal to 224 imperial gallons (269 US gal; 1,020 L), the volume occupied by a mass of 1 long ton (1.12 ST; 1.02 t) under the conditions that define 1 imperial gallon (1.20 US gal; 4.55 L).
Note that these are small calories (cal). The dietary calorie (Cal) is distinct and equal to one kilocalorie.
Early values for the explosive energy released by trinitrotoluene (TNT) ranged from 900 to 1100 calories per gram. In order to standardise the use of the term TNT as a unit of energy, an arbitrary value was assigned based on 1000 calories (1 kcal or 4.184 kJ) per gram. Thus there is no longer a direct connection to the chemical TNT itself. It is now merely a unit of energy that happens to be expressed using words normally associated with mass (e.g., kilogram, tonne, pound).[11][12] The definition applies for both spellings: ton of TNT and tonne of TNT.
Measurements in tons of TNT have been used primarily to express nuclear weapon yields, though they have also been used since in seismology as well.
The unit ton is used in refrigeration and air conditioning to measure heat absorption. Prior to the introduction of mechanical refrigeration, cooling was accomplished by delivering ice. Installing one ton of refrigeration replaced the daily delivery of one ton of ice.
The refrigeration ton is commonly abbreviated as RT.