How to Convert Centimetres to Millimetres (cm to mm)
Length conversions come up when reading overseas furniture specs, cycling the Round Island Route in kilometres while a foreign app shows miles, or checking marine distances in the Singapore Strait in nautical miles. This guide shows how to convert centimetres into millimetres by hand, with examples and a quick-reference table.
The conversion
To convert centimetres to millimetres, multiply the value by 10. To go the other way, divide by the same number (or multiply by 0.1). For a quick estimate, multiply by about 10.
Millimetres = centimetres × 10
Worked examples
- 3 cm = 30 mm
- 12.5 cm = 125 mm
- 75 cm = 750 mm
Centimetres to Millimetres table
| Centimetres | Millimetres |
|---|---|
| 1 cm | 10 mm |
| 2 cm | 20 mm |
| 5 cm | 50 mm |
| 10 cm | 100 mm |
| 20 cm | 200 mm |
| 25 cm | 250 mm |
| 50 cm | 500 mm |
| 100 cm | 1,000 mm |
| 250 cm | 2,500 mm |
| 500 cm | 5,000 mm |
| 1,000 cm | 10,000 mm |
Common questions
Is cm to mm exact?
The factors used here are the internationally defined values where they exist; results are rounded for display only.
How do I convert back?
Use the Millimetres to Centimetres converter.
Mistakes to avoid
Multiplying when you should divide
Converting to a smaller unit gives a bigger number, and converting to a larger unit gives a smaller one. If your answer moves the wrong way, you have inverted the factor.
Rounding the factor too early
Using 3 instead of 3.28 for feet per metre introduces an error of almost 9% before you have started.
Dropping the units
A bare number without a unit is easy to misread later. Always write the unit with the result.
Background
A conversion table is handy for common values, but a calculator is faster and avoids interpolation errors for anything in between.
Unit conversion is simply multiplication by a fixed ratio. The ratio between two units of the same quantity never changes, so once you know it you can convert any value in either direction.
Many conversion factors are exact by definition. The inch has been defined as exactly 2.54 centimetres since 1959, and the pound as exactly 0.45359237 kilograms, so conversions involving them can be as precise as you need.
For any value, use the Centimetres to Millimetres Converter or browse all length converters.
Run your own numbers: Centimetres to Millimetres Converter