The millimetre (international spelling; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand millimetres in a metre. There are ten millimetres in a centimetre.

Ruler with millimetre and centimetre marks
General information
Unit systemSI
Unit ofLength
Named afterThe metric prefix mille (Latin for "one thousand") and the metre
1 mm in ...... is equal to ...
   micrometres   1×103 μm = 1000 μm
   centimetres   1×10−1 cm = 0.1 cm
   metres   1×10−3 m = 0.001 m
   kilometres   1×10−6 km
   inches   0.039370 in
   feet   0.0032808 ft
Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter.

One millimetre is equal to 1000 micrometres or 1000000 nanometres. Since an inch is officially defined as exactly 25.4 millimetres, a millimetre is equal to exactly 5127 (≈ 0.03937) of an inch.

Share this article:

This article uses material from the Wikipedia article Millimetre, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.