The tonne (British and SI; or metric ton (in the United States) is a non-SI metric unit of mass equal to or one megagram (Mg); it is equivalent to approximately  pounds, or 0.984 long tons (imperial). Although not part of the SI per se, the tonne is "accepted for use with" SI units and prefixes by the International Committee for Weights and Measures, along with several other units like the bar, litre and day.

Tonne is a metric unit of weight.