A ton stands for a short ton mainly in the US, a long ton in the UK, or a metric ton in some other countries. On the other hand, a tonne means only a metric ton.
 A metric ton weighs exactly 1000 kilograms.
A US ton or short ton weighs around 907.185 kilograms.
An imperial ton or long ton weighs about 1016.047 kilograms.
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