How do I convert mm to cm?
Type a value in either box, and the answer shows it in the other unit as you type.
- Centimeters (cm)
- 0.1
1 mm = 0.1 cm.
Centimeters (cm): 0.1. 1 mm = 0.1 cm.
Centimeters (cm) by millimeters (mm)
How to calculate
Converts millimeters (mm) to centimeters (cm) and back, with the exact unit definitions.
Example with the default inputs (Millimeters (mm) 1): 1 mm = 0.1 cm.
Formula: cm = mm × 0.1
- 1 millimeter = 0.1 centimeters, 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.
- Millimeters (mm) 1 gives Centimeters (cm) 0.1.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
- Millimeters (mm) 25.4 gives Centimeters (cm) 2.54.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
- Centimeters (cm) 2.54 gives Millimeters (mm) 25.4.Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8
Other questions people ask
How many centimeters are in a millimeter?
1 millimeter is 0.1 centimeters, from the exact unit definitions (NIST SP 811).
How do I convert mm to cm?
Multiply by 0.1: cm = mm × 0.1. For example, 1 mm × 0.1 = 0.1 cm.
How do I convert cm back to mm?
Multiply by 10, or type the centimeters into the second box and the converter works it out. 1 centimeter is 10 millimeters.
What is 25.4 mm in cm?
2.54 cm, exactly 1 inch: 25.4 ÷ 10. Milli means one thousandth and centi one hundredth (NIST SP 811).