Millimeter (mm)
Definition
One thousandth of a meter (10⁻³ m).
History
The millimeter is one thousandth of a meter, defined with the rest of the decimal metric system in the 1790s. Its small size suits precise work.
Where it is used
Millimeters are used for rainfall, engineering tolerances, and the sizes of screws, hardware and printed parts.
Typical uses include rainfall, engineering tolerances, screws and hardware.
Conversion pages
These pages convert millimeter to or from another unit in length.
Other Length units
Sources
- BIPM SI BIPM, The International System of Units (SI), 9th ed. (2019) · Dataset reviewed Nov 11, 2026