The millimetre (American spelling: millimeter, symbol mm) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length. Equal to 1000 micrometres. Equal to 1000000 nanometres. Unicode symbols For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for: millimetre (㎜) - code 339C square millimetre (㎟) - code 339F cubic millimetre (㎣) - code 33A3 They are useful only with Ea… (More on Millimeter)