# Millimeters to centimeters converter

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

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

Millimeter readings are useful for small clearances, fasteners and drawing dimensions. Retain the tolerance with the original measurement: converting the number cannot make a manufactured part more accurate. Check whether a nominal part size describes its actual measured diameter.

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

The millimetre is one thousandth 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

- **Millimeters (mm)**

## Results

- Centimeters (cm) — main result
- Conversion
- 1 cm in millimeters (mm)

## Formula

$$
\text{centimeters} = \text{millimeters} \times 0.1
$$

## Worked examples

### 25 mm to cm

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

### 15 mm to cm

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

### 100 mm to cm

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

## Questions

### When would I convert mm to cm?

Millimeter readings are useful for small clearances, fasteners and drawing dimensions. Retain the tolerance with the original measurement: converting the number cannot make a manufactured part more accurate. Check whether a nominal part size describes its actual measured diameter.

### How many centimeters are in a millimetre?

One millimetre is exactly 0.1 centimeters. The millimetre is one thousandth of a metre, the SI base unit of length.

### How do you convert mm to cm?

Multiply the number of millimeters by 0.1. For example, 25 mm × 0.1 = 2.5 cm. To go the other way, divide by 0.1.

### How accurate is the millimeters to centimeters 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, “25 mm to cm” 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)