The word most likely comes from the Latin word tunna, which is a word for a cask. Since a large cask full of something would weigh roughly a metric ton, this origin is commonly accepted. The word has been in use for quite some time, although previously the spelling was more often tunne.
The metric ton is often spelled as tonne, and in the United States may also be called a tonneau. A metric ton is not to be confused with the short ton unit, known simply as a ton in the system used in the United States. This ton is equal to 2000 pounds, or roughly 907kg. It should also not be confused with a long ton, a unit no longer in common usage in the United States, which is equal to 2240 pounds.
The official symbol for the metric ton in the International System of Units (SI) is simply ‘t’. Although all of the standard prefixes can be used with the metric ton, in practice the most common ones are the same ones used with the short ton. The kilotonne and megatonne are the only two units commonly seen outside of the metric ton itself.
Kilotonne and megatonne may be used as metric for measuring energy release. This makes use of the metric ton by connecting it with the explosive TNT, as a way of calculating the force of an explosion. A metric ton of TNT releases roughly 4.19 X 10^9 Joules of energy, with a kilotonne releasing 4.19 X 10^12, and a megatonne releasing 4.19 X 10^15. To put this in some context, the Hiroshima bomb was equal to about twenty kilotonnes of TNT, while a modern nuclear missile could fall closer to the twenty megatonne range.
Because of the similarity in pronunciation — and in some circles, spelling — there can often be confusion between a short ton, a long ton, and a metric ton. In general, in the metric-using world the term ton or tonne alone will be used to refer to a metric ton, while the distinction long ton or short ton will be used to refer to the measure of the standard or Imperial system. In the United States, the term ton will be used to refer to a short ton, although in some industries — such as freight — a ton may be assumed to be a long ton. The term metric ton is then used to distinguish the metric unit. As a rule of thumb, it is a good idea to distinguish which unit of measurement you intend, if there is any doubt that your listeners might misconstrue your meaning.
