ton

   1. (tn or T or t)

   a traditional unit of weight equal to 20 hundredweight.

   In the United States and Canada, there are 100 pounds in the hundredweight and exactly 2000 pounds (907.185 kilograms) in the ton. In Britain, there are 112 pounds in the hundredweight and 2240 pounds (1016.047 kilograms) in the ton. To distinguish between the two units, the British ton is called the long ton and the American one is the short ton. In old England, a "tun" was a large cask used to store wine. Because these tuns were of standard size, more or less, the tun came to represent both a volume unit, indicating the capacity of a cask, and also a weight unit, indicating the weight of a cask when it was full. The best symbol to use for this unit is tn. In the U.S. mining industry, T is used to distinguish the traditional ton from the metric ton, but T is the SI symbol for the tesla. The symbol t, traditionally used for the long or short ton, is now reserved for the metric ton.

   2. (t)

   a metric unit of mass, equal to 1000 kilograms, or approximately 2204.623 pounds avoirdupois. This metric ton is a bit smaller than the British long ton. The metric ton is now known officially as the tonne (see below).

   3. (RT or rT)

   a unit used traditionally to measure the cargo capacity of a merchant ship. During the Middle Ages, merchant ships were rated by the number of tuns of wine they could carry. Today the merchant marine ton is defined to be exactly 100 cubic feet, or approximately 2.8316 cubic meters. This unit is often called the register ton, since it is recorded in official registers of ships. The symbol RT seems to be in wide use for this unit, but it is also used for the refrigeration ton (definition⁷ below).

   4. (DT or dT)

   a unit of volume used traditionally to measure the "displacement" of ships, especially warships. One way to describe the size of a ship is to state the volume of sea water it displaces when it is afloat: in other words, the volume of that part of the ship below the waterline. The actual weight of sea water varies somewhat according to its temperature and how salty it is, but for this purpose it has been agreed that a long ton of sea water occupies about 35 cubic feet. Accordingly the displacement ton is defined to be exactly 35 cubic feet, or approximately 0.9911 cubic meter. Since this is a much smaller unit than the register ton, warships have a much higher "tonnage" than merchant ships of approximately the same dimensions. The symbol DT is recommended for this unit.

   5. (FT)

   a traditional unit of volume used for measuring the cargo of a ship, truck, train, or other freight carrier. This freight ton is exactly 40 cubic feet, or approximately 1.13267 cubic meters. However, the term "freight ton" is also being used to mean a metric ton of freight, volume not specified. Perhaps because of this confusion, the 40 cubic foot unit is often called the measurement ton (MTON). But the confusion seems impossible to dispel; some shippers are now using "measurement ton" to mean a metric ton of freight. To further complicate the situation, the freight ton is also called the U.S. shipping ton; the British shipping ton is 5% larger at 42 cubic feet (1.1893 cubic meters). Yet another name is the cubic ton.

   6. (tn or T)

   a unit of energy used for measuring the energy of an explosion, especially a nuclear explosion. In this usage, one ton is supposed to be the amount of energy released by the explosion of one short ton of TNT. This is defined in the U.S. to equal exactly 4.184 gigajoules (GJ) or roughly 4 million Btu.

   7. (RT)

   a unit of power used in refrigeration engineering. One ton of refrigeration is intended to be the power required to freeze one short ton of water at 0°C in 24 hours. This is assumed to be exactly 12 000 Btu per hour (Btu/h or "Btuh"), which is equivalent to 200 Btu/min, 3.516 853 kilowatts, 4.7162 horsepower, or 0.8396 (kilogram) Calorie per second (Cal/s). The symbol RT seems to be in wide use for this unit, but it is also used for the register ton (definition³ above).

   8. British slang for 100, especially the sum of 100 pounds (currency), a speed of 100 miles per hour, or a score of 100 in darts or cricket. The origin of this usage is not clear.