# Millimeters to Centimeters (mm to cm)

> Convert millimeters to centimeters: 1 mm = 0.1 cm. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `mm-to-cm` · Quantity: Length (`length`, base unit m) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/mm-to-cm · This document: https://tttkmbb.com/conversion/mm-to-cm.md · JSON: https://tttkmbb.com/conversion/mm-to-cm.json (add `?value=` for a result)

## Formula

- `1 mm = 0.1 cm`
- `centimeters = millimeters × 0.1`
- Reverse: `millimeters = centimeters × 10`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 mm = 0.5 cm
- 12.5 mm = 1.25 cm
- 100 mm = 10 cm

## Conversion table

| Millimeters (mm) | Centimeters (cm) |
| --- | --- |
| 1 | 0.1 |
| 2 | 0.2 |
| 3 | 0.3 |
| 4 | 0.4 |
| 5 | 0.5 |
| 6 | 0.6 |
| 7 | 0.7 |
| 8 | 0.8 |
| 9 | 0.9 |
| 10 | 1 |
| 15 | 1.5 |
| 20 | 2 |
| 25 | 2.5 |
| 30 | 3 |
| 40 | 4 |
| 50 | 5 |
| 75 | 7.5 |
| 100 | 10 |
| 200 | 20 |
| 250 | 25 |
| 500 | 50 |
| 1000 | 100 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=mm&to_unit=cm` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"mm","to_unit":"cm"}`
- All length units: https://tttkmbb.com/api/v1/units?quantity=length · full converter: [Length Converter](https://tttkmbb.com/conversion/length.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many centimeters are in one millimeter?**

1 mm = 0.1 cm. The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.

**What is the formula to convert millimeters to centimeters?**

Multiply the value in millimeters by 0.1: centimeters = millimeters × 0.1. For example, 5 mm = 0.5 cm.

**How do I convert centimeters back to millimeters?**

Multiply by the inverse factor 10 (millimeters = centimeters × 10), or use the centimeters-to-millimeters page.

## Related conversions

- [Centimeters to millimeters](https://tttkmbb.com/conversion/cm-to-mm.md) (reverse)
- [Kilometers to Miles](https://tttkmbb.com/conversion/km-to-miles.md)
- [Miles to Kilometers](https://tttkmbb.com/conversion/miles-to-km.md)
- [Meters to Feet](https://tttkmbb.com/conversion/meters-to-feet.md)
- [Feet to Meters](https://tttkmbb.com/conversion/feet-to-meters.md)
- [Centimeters to Inches](https://tttkmbb.com/conversion/cm-to-inches.md)
- [Inches to Centimeters](https://tttkmbb.com/conversion/inches-to-cm.md)
- [Millimeters to Inches](https://tttkmbb.com/conversion/mm-to-inches.md)
- [Inches to Millimeters](https://tttkmbb.com/conversion/inches-to-mm.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)