Difference between Millimetre and Millimeter

What is the difference between Millimetre and Millimeter?

Millimetre as a noun is an si/mks unit of measure, the length of 1/1000 of a metre. symbol: mm while Millimeter as a noun is an si/mks unit of measure, the length of 1/1000 of a meter. symbol: mm

We hope you now know whether to use Millimetre or Millimeter in your sentence.