To convert centimeters to millimeters (cm to mm), multiply by 10. 1 centimeter equals 10 mm, about 1.7 times as much as a grain of rice.
| centimeters | millimeters |
|---|---|
| 1 centimeter | 10 mm |
| 2 centimeters | 20 mm |
| 5 centimeters | 50 mm |
| 10 centimeters | 100 mm |
| 25 centimeters | 250 mm |
| 50 centimeters | 500 mm |
| 100 centimeters | 1,000 mm |
| 250 centimeters | 2,500 mm |
| 500 centimeters | 5,000 mm |
| 1000 centimeters | 10,000 mm |
Definition: 1/100 of a meter - the "centi" prefix doing the same job it does in "century" or "cent."
History: Introduced alongside the meter itself during the French Revolution's metric overhaul, the centimeter was designed from the start to be a convenient, everyday-sized subdivision - a meter is often too big and a millimeter too small for describing things like a person's height or a book's thickness.
Current use: Height, everyday object sizes, and fabric measurements across most of the world; also the standard unit doctors use internationally for body measurements.
Definition: 1/1000 of a meter - the same "milli" prefix as milliliter or milligram.
History: Like the centimeter, it arrived as part of the same 1790s French decimal system, built specifically to make precise, small-scale measurement simple - no more converting between competing local systems of inches, lines, and points.
Current use: Engineering tolerances, screen and camera specs, and rainfall measurements - which is why weather reports outside the US say "20mm of rain" rather than inches.
The factor is 10.0000, which is derived rather than defined, so any decimal you see has been rounded somewhere.
For mental arithmetic the factor is close enough to 10 to use directly: multiply centimeters by 10 and the answer is right to within a rounding error.
The reverse factor is 0.1, so one millimeter is that many centimeters. Two decimal places is plenty for most purposes, and three is more than a tape measure can justify.
To anchor the scale: 1 centimeter is about 10 mm.