How do I convert cm to mm?
Type a value in either box, and the answer shows it in the other unit as you type.
- Millimeters (mm)
- 10
1 cm = 10 mm.
Millimeters (mm): 10. 1 cm = 10 mm.
Millimeters (mm) by centimeters (cm)
How to calculate
Converts centimeters (cm) to millimeters (mm) and back, with the exact unit definitions.
Example with the default inputs (Centimeters (cm) 1): 1 cm = 10 mm.
Formula: mm = cm × 10 (the same as cm ÷ 0.1)
- 1 centimeter = 10 millimeters, from the exact definitions in NIST SP 811.
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up; an answer of 1 billion or more shows at most 15 significant digits.
Worked examples
Each example is checked against the calculator on every build.
- Centimeters (cm) 1 gives Millimeters (mm) 10.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
- Centimeters (cm) 2.5 gives Millimeters (mm) 25.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
- Millimeters (mm) 25 gives Centimeters (cm) 2.5.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
Other questions people ask
How many millimeters are in a centimeter?
1 centimeter is 10 millimeters, from the exact unit definitions (NIST SP 811).
How do I convert cm to mm?
Multiply by 10: mm = cm × 10 (the same as cm ÷ 0.1). For example, 1 cm × 10 = 10 mm.
How do I convert mm back to cm?
Multiply by 0.1, or type the millimeters into the second box and the converter works it out. 1 millimeter is 0.1 centimeters.
What is 2.5 cm in mm?
25 mm: 2.5 × 10. Centi means one hundredth and milli one thousandth (NIST SP 811), so 1 cm is 10 mm.