Definitions

shipping ton

Ton

[tuhn]

Units of mass

There are three similar units of mass called the ton:

  1. long ton (simply ton in countries such as the United Kingdom which formerly used the Imperial system of weights and measures) is a weight ton or gross ton, and is 2,240 pounds (exactly 1,016.0469088 kg). In the UK and most of the areas which used the Imperial system, the metric ton (1,000 kg), which is conveniently very similar to—less than 2% difference—is the only form of ton legal for trade.
    • In the iron industry in the 17th century and 18th century, a ton shortweight was the standard 2,240 lb, whereas a ton longweight was 2,400 lb (the hundredweight being 120 lb).
    • The long ton is used for petroleum products such as aviation fuel.
    • Deadweight ton (abbreviation 'DWT' or 'dwt') is a measure of a ship's carrying capacity, including bunker oil, fresh water, ballast water, crew and provisions. It is expressed in metric tons (1,000 kg) or long tons (2,240 pounds, about 1,016 kg). This measurement is also used in the U.S. tonnage of naval ships.
    • Increasingly, metric tonnes are being used rather than long tons in measuring the displacement of ships. See tonnage.
  2. short ton (usually called simply ton in North America or sometimes called a net ton) = 2,000 lb (about 907.18474 kg).
    • Harbour ton used in South Africa in the 20th century, equal to 2000 pounds or one short ton.
  3. The metric ton, or tonne, is 1,000 kg (or 1 Mg) or approximately 2,204.6 pounds.

Both the long ton and the short ton are composed of twenty hundredweights, each having different values for the hundredweight (112 and 100 pounds respectively). Prior to the 15th century in England, the ton was composed of 20 hundredweights, each of 108 lb, giving a ton of 2,160 pounds.

Assay ton (abbreviation 'AT') is not a unit of measurement (nobody ever has x assay tons of something), but rather 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; however, in more recent documents the spelling tonne refers exclusively to the metric ton.

In the context of nuclear power plants, tHM and MTHM mean (metric) tonnes of heavy metals, and MTU means metric tonnes of uranium. In the steel industry, the acronym THM has the meaning '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.

Common abbreviations

In the U.S. mining industry, 'T' is used to distinguish the traditional ton from the metric ton, but 'T' is also the SI symbol for the tesla. The symbol 't', traditionally used for the long or short ton, is now reserved for the metric ton.

Units of force

There are also the units of force based on each of these three mass units, but none are acceptable for use with SI. The tonne force, like the kilogram force, is no exception. Only the tonne as a unit of mass is acceptable for use with SI.

  • 1 short ton force = 2000 pounds-force (lbf) = 8.896443230521 kilonewtons (kN)
  • 1 long ton force = 2240 lbf = 9.96401641818352 kN
  • 1 tonne force = 1000 kgf = 9.80665 kN

Units of volume

Also see tonnage.

The displacement ton is a unit of volume used for describing the displacement of (usually) a warship. It represents the volume of water displaced by the ship. One measurement ton is equal to 35 cubic feet or 0.99108963072+ cubic metres. Coincidentally, 35 cubic feet of water weighs very close to 1 tonne, but the tonne had not been defined when the displacement ton was. Consequently it is less approximately equal to 1 long ton of water (2240 lbs). It is usually abbreviated as DT.

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 today equal to 40 cubic feet of space (1.132 cubic metres), 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 metric ton or even the megaton.

The register ton is also a unit of volume used for the cargo capacity of a ship, defined as 100 cubic feet (roughly 2.83 cubic metres). 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 about 1.88 cubic yards.

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 equal to 224 imperial gallons (the volume occupied by a mass of one long ton under the conditions which define the imperial gallon).

See 1 E-1 m³ and orders of magnitude (volume) for a comparison with other volumes.

(Note that volume tons are units of convenience used in shipping and are not useful in science except that they are exactly defined.)

Units of energy and power

Ton of TNT

  • A ton of TNT or tonne of TNT is a unit of energy equal to 109 (thermochemical) calories, also known as a gigacalorie (Gcal), equal to 4.184 gigajoules (GJ).
  • A kiloton of TNT or kilotonne of TNT is a unit of energy equal to 1012 calories, also known as a teracalorie (Tcal), equal to 4.184 terajoules (TJ).
  • A megaton of TNT (1,000,000 metric tonnes) or megatonne of TNT is a unit of energy equal to 1015 calories, also known (infrequently) as a petacalorie (Pcal), equal to 4.184 petajoules (PJ).

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, 4.184 kilojoules) 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

  • A ton of coal equivalent or tonne of coal equivalent (TCE), a conventional value of 7 Gcal (IT) = 29.3076 GJ.

Ton of oil equivalent

  • A ton of oil equivalent or tonne of oil equivalent (TOE), a conventional value of 10 Gcal (IT) = 41.868 GJ ≈ 10.0067 ton of TNT. See also GTOE.

Refrigeration

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.

  • In North America, a standard ton of refrigeration is 12,000 BTU/h = 200 BTU/min ≈ 3.51685 kW. This is approximately the power required to melt one short ton (2,000 lb) of ice at 0 °C 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 1 °F every 10 minutes = 13,440 BTU/h ≈ 3,939 W.

The refrigeration ton is abbreviated as RT providing scope for confusion with the register ton.

Truck classes

When light-duty trucks were first produced, they were rated by their payload capacity in tons (e.g., -, - and 1-ton). The Ford F-150, Chevy/GMC 1500, and Dodge 1500 are a -ton. The Ford F-250, Chevy/GMC 2500, and Dodge 2500 are a -ton. The Ford F-350, Chevy/GMC 3500, and Dodge 3500 are a 1-ton. But throughout the years, the payload capacities have increased while the ton title has stayed the same. The current ton rating scheme is nothing more than just a generic truck name.

Miscellaneous tons

  • Ton is also used informally to mean a large amount of something (material or not), for example, "We've been having a ton of good luck recently".
  • In Britain, ton is colloquially used to refer to 100 of a given unit. Ton can thus refer to the speed of motor vehicles, namely to the speed of 100 miles per hour e.g. "Lee was doing a ton down the motorway", to money e.g. "How much did you pay for that?" "A ton" (£100), to 100 points in a game e.g. "Eric just threw a ton in our darts game" or to a hundred of pretty much anything else.

A ton is also equivalent to 100 runs in the game of cricket (more commonly known as a century).

See also

References

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