Ton vs Metric Ton
Ton and metric ton are units of measurement but there is difference between the two. Metric ton is a unit based upon SI system and is equal to 1000 kilos. Thus it is a megagram as it contains 1 million grams. Why the words ton and metric ton are being used is interesting to note. The word ton is derived from Latin tunna which means a cask. As in earlier times a cask full of an item normally weighed nearly a metric ton, the word ton stuck.
A metric ton is not the same as short ton which is what is used in the US. The ton that is used in the US translates into 2000 pounds, or roughly 907 kg. The long ton (tonne) is equivalent to 2240 pounds but it is not used commonly in the US.
In English speaking countries, the spelling tonne is commonly used as a measurement of weight. In Britain for example, prior to the introduction of the SI system, the ton that was used was equal to 2240 pounds (1016kg), and since this value is very close to actual metric tonne (1000kg), people felt very little difference between the earlier ton and the metric tonne. This is why people in Britain continued to use the same old spelling. However, it was US, where the difference was felt, and unless otherwise mentioned, a ton means 2000 pounds or 907 kg.