A ton is a metric unit of measurement equivalent to 1,000 kilograms, but in the US, “ton” usually refers to the non-metric “short ton” or “long ton.” The US Customary Units are similar to the imperial system used in the UK. The ton is sometimes used to measure energy release and force, but the SI unit for force is the newton. The word “ton” likely comes from the Latin term for a barrel.
A ton is a unit of measurement based on the metric system, rather than the standard, or imperial, system more commonly used in the United States. It is known as a ton in most other countries and is equivalent to 1,000 kilograms. Strictly speaking, it is a megagram, or a million grams.
Use
In countries that use the metric system, tonne is the correct term for this unit of measurement, although it is often referred to as a ton. In the United States, however, “ton” usually means another, non-metric unit known as a “short ton” – equivalent to 2,000 pounds – or, less commonly, a “long ton” – 2,240 pounds – which is the same as the imperial ton formerly used in the UK. In the United States, this measure is still used in the freight sector and for naval vessels. Due to the similarity in pronunciation and, in some cases, spelling, short, long and metric tons can often be confused. The terms “long” and “short” derive from units used in the UK before conversion to the metric system and are largely obsolete outside the United States.
Conversions
Because of the different systems and terminology used by the United States and other countries, and in the United States for different applications, it is useful to be able to convert one unit to another. The main conversions and synonyms are summarized below:
Equivalent Terms and Conversions
USA UK Kilograms Pounds
Metric ton Ton 1.000 2.205
Short Ton Ton 907 2,000
Long ton Imperial ton 1.016 2.240
Measurement systems and SI units
The system of measurement employed in the United States, known as the US Customary Units, is very similar to the imperial system employed in the United Kingdom prior to the adoption of metric units. There are, however, some differences: these arise from the fact that the system is based on UK units which were in use before the imperial system was standardised. The short ton was adopted in the United States prior to the UK’s imperial standardization, after which the imperial unit became the slightly heavier long ton. The ton was sometimes referred to as a tonneau or millier – both French terms – but these are no longer used.
It has been recommended that the United States switch completely to the metric system. This, however, has met with considerable resistance from trade and consumers. Consequently, metric measurements are normal only for scientific, medical, and military purposes, and the short ton is still the standard for common use.
The official symbol for the ton in the International System of Units (SI) is simply “t”. While the unit itself is not an SI unit, it is accepted for use with the SI system. All of the standard prefixes can be used with it, but in practice the most common are kilotonne and megatonne.
Measure energy and strength
The units kilotonne and megatonne can be used to measure energy release. In this context, energy is related to the amount released by the detonation of the equivalent mass of trinitrotoluene (TNT), an explosive used in bombs during World War II. These units are most commonly used to measure the explosive power of nuclear weapons. A ton of TNT releases approximately 4.19 x 109 joules of energy, with a kiloton releasing 4.19 x 1012 and a megaton releasing 4.19 x 1015. To put this in context, the Hiroshima bomb was equal to about twenty kilotons of TNT, while a modern nuclear missile could drop closer to twenty megatons.
The ton is sometimes used as a unit of force. Strictly speaking, it should be called a ton-force, but it is often simply called a ton or, in the US, a metric ton. For example, one could state that a bulldozer can exert a force of ten tons. The SI unit for force, however, is the newton, and the ton or ton-force are not accepted as part of the SI system.
Origin
The word most likely comes from the Latin term tunna, which is the word for a barrel. Since a large barrel full of, say, wine would weigh roughly a ton, this origin is commonly accepted. The word has been in use for quite some time, although previously the spelling was more often tunne.
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