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 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 (800 to 1000 L), which could weigh around 2,000 pounds (900 kg) and occupy some 60 cubic feet (1700 L) of space.

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 (avoirdupois pounds). In the United States and Canada, however, a ton is defined to be . 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 . 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 35 to 100 cu ft (around 1000 to 2800 L) in capacity.

It can also be used as a unit of energy, expressed as an equivalent of coal burnt, TNT detonated, or in refrigeration, ice melted.

Units of mass/weight

::Note 1: The longweight and shortweight tons were used as a means of making an allowance for wastage in an industrial process. The workman is provided with a longweight ton and is expected to return a shortweight ton of processed product. These measures were particulary used in the operation of hammering iron blooms into shape. ::Note 2: In other industries, a different longweight ton might be used. Coal miners delivered coal to the surface in longweight tons but were paid only for a shortweight ton. This was supposedly to allow for "dirt" (non-coal rocks) in the output. Mine owners, however, were free to set the value of the longweight ton at a value of their own choosing, and in at least some cases, it was set to () compared to the shortweight ton. This was a source of discontent amongst the miners who saw the practice as unfairly in favour of the mine owners.

;Others

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 .

Assay ton (abbreviation 'AT') is not a unit of measurement, but a standard quantity used in assaying ores of precious metals; it is grams (short assay ton) or 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.

Units of volume

The displacement ton is a unit of volume used for calculating the displacement of a ship. 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. It equates to of sea water at average density, being slightly less than the 224 imperial gallons, of the water ton (qv). It is usually abbreviated as DT.

One measurement ton or freight ton is equal to , but historically it has had several informal definitions. It is sometimes abbreviated as "MTON". 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 correctly abbreviated as "FT" but some users are now using freight ton to represent a weight of , 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 megatonne.

The register ton is a unit of volume used for the cargo capacity of a ship, defined as . 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 .

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.

The water ton was formerly used in Great Britain and is equal to , the volume occupied by a mass of under the conditions that define .

Units of energy and power

Ton of TNT

Note that these are small calories (cal). The dietary calorie (Cal) is distinct and equal to one kilocalorie (Kcal), and is gradually being replaced by the latter correct term.

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 () 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). 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.

Ton of coal equivalent

Refrigeration

In North America, a standard ton of refrigeration is . "The heat absorption per day is approximately the heat of fusion of 1 ton of ice at ." This is approximately the power required to melt one short ton () of ice at in 24 hours, thus representing the delivery of 1 ton of ice per day. A less common usage is the power required to cool 1 long ton () of water by every 10 minutes = 13,440 BTU/h ≈ 3939 W.

A Refrigeration Ton should be regarded as power produced by a chiller when operating in standard ARI conditions, which are typically for chilled water unit, and air entering the condenser. This is commonly referred to as "true ton". Manufacturers can also provide tables for chillers operating at other chilled water temperature conditions (as ) which can show more favorable data, which are not valid when making performance comparisons among units unless conversion rates are applied.

The refrigeration ton is commonly abbreviated as RT.

Informal tons

See also

References

Category:Units of mass Category:Units of volume Category:Customary units in the United States Category:Imperial units