Millimetre

The millimetre (SI symbol: mm; international spelling) or millimeter (American spelling) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, the SI base unit of length.

• 1 metre = 1000 millimetres
• 1 centimetre = 10 millimetres

One millimetre is also equal to:

• 1000micrometres
• 1000000nanometres

Since an inch is officially defined as exactly 25.4 millimetres, 1 millimetre is precisely 5⁄127 inches (≈ 0.03937 inches).