# Centimeters to millimeters converter

> Convert centimeters to millimeters (cm to mm) with the exact factor, a conversion chart and worked steps.

Interactive version: https://www.calcopenly.com/conversion/cm-to-mm
Subject: Unit converters

A centimeter measurement often comes from a tape used for furniture, clothing or body height. Keep the full reading, including a decimal part, when comparing it with a specification written in another unit. A decimal length is different from a feet-and-inches notation.

One centimetre is exactly 10 millimeters, so 2.5 cm is 25 mm. To convert cm to mm, multiply by 10; to convert back, multiply by 0.1.

The centimetre is one hundredth of a metre, the SI base unit of length. Because both units are defined exactly, the factor above is exact and the results here carry no conversion error.

## Inputs

- **Centimeters (cm)**

## Results

- Millimeters (mm) — main result
- Conversion
- 1 mm in centimeters (cm)

## Formula

$$
\text{millimeters} = \text{centimeters} \times 10
$$

## Worked examples

### 2.5 cm to mm

- Centimeters (cm): 2.5 cm
- **Millimeters: 25 mm**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

### 1.5 cm to mm

- Centimeters (cm): 1.5 cm
- **Millimeters: 15 mm**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

### 10 cm to mm

- Centimeters (cm): 10 cm
- **Millimeters: 100 mm**
- Checked against: Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions)

## Questions

### When would I convert cm to mm?

A centimeter measurement often comes from a tape used for furniture, clothing or body height. Keep the full reading, including a decimal part, when comparing it with a specification written in another unit. A decimal length is different from a feet-and-inches notation.

### How many millimeters are in a centimetre?

One centimetre is exactly 10 millimeters. The centimetre is one hundredth of a metre, the SI base unit of length.

### How do you convert cm to mm?

Multiply the number of centimeters by 10. For example, 2.5 cm × 10 = 25 mm. To go the other way, divide by 10.

### How accurate is the centimeters to millimeters converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 3 worked examples whose answers come from independent sources; for example, “2.5 cm to mm” is checked against Exact-fraction computation from the legal unit definitions (scripts/gen-pairs.py, Python fractions).

### Where does the method come from?

NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B; NIST Handbook 44, Appendix C: General tables of units of measurement; BIPM, The International System of Units (SI Brochure), 9th edition.

## Sources

- [NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C: General tables of units of measurement](https://www.nist.gov/pml/weights-and-measures/publications/nist-handbooks/handbook-44)
- [BIPM, The International System of Units (SI Brochure), 9th edition](https://www.bipm.org/en/publications/si-brochure)