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Millimetres

Millimetre
Unit system metric
Unit of length
Symbol mm 
Unit conversions
1 mm in ... ... is equal to ...
   SI units    1×10−3 m
   imperial/US units    0.0032808 ft
0.039370 in

The millimetre (International spelling as used by the International Bureau of Weights and Measures; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length.

It is equal to 1000 micrometres or 1000000 nanometres. A millimetre is equal to exactly 5127 (approximately 0.039370) of an inch.

Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second". A millimetre, 1/1000 of a metre, is therefore the distance travelled by light in 1/299792458000 of a second.


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