---
title: "21 mm to cm = 2.1 cm"
description: "21 millimeters is 2.1 centimeters. The arithmetic, a table of nearby values, and a converter for any other number."
url: https://atoneplace.net/convert/21-mm-to-cm/
site: "At One Place"
---

# 21 mm to cm

**21 millimeters in centimeters: 21 mm = 2.1 cm**

cm = mm × 1/10

21 millimeters is 2.1 centimeters. To get there, multiply by 0.1.

## Values either side

*Millimeters near 21, converted to centimeters.*

| Millimeters | Centimeters |
| --- | --- |
| 17 mm | 1.7 |
| 18 mm | 1.8 |
| 19 mm | 1.9 |
| 20 mm | 2 |
| 21 mm ← | 2.1 |
| 22 mm | 2.2 |
| 23 mm | 2.3 |
| 24 mm | 2.4 |
| 25 mm | 2.5 |

## How the conversion works

The relationship is cm = mm × 1/10. Both units measure length, so the conversion is a fixed factor that never changes.

## Common questions

### What is 21 mm in centimeters?

21 mm is 2.1 cm.

### How do you convert millimeters to centimeters?

Multiply by 0.1.

## Related pages

- [Millimeters to centimeters](https://atoneplace.net/convert/mm-to-cm/)
- [21 cm to mm](https://atoneplace.net/convert/21-cm-to-mm/)
- [17 mm to cm](https://atoneplace.net/convert/17-mm-to-cm/)
- [18 mm to cm](https://atoneplace.net/convert/18-mm-to-cm/)
- [19 mm to cm](https://atoneplace.net/convert/19-mm-to-cm/)
- [20 mm to cm](https://atoneplace.net/convert/20-mm-to-cm/)
- [22 mm to cm](https://atoneplace.net/convert/22-mm-to-cm/)
- [23 mm to cm](https://atoneplace.net/convert/23-mm-to-cm/)
- [24 mm to cm](https://atoneplace.net/convert/24-mm-to-cm/)
- [25 mm to cm](https://atoneplace.net/convert/25-mm-to-cm/)

## Sources

- Guide for the Use of the International System of Units (SP 811) — NIST (https://www.nist.gov/pml/special-publication-811) [Public domain (US Government)]
- The International System of Units (SI Brochure) — Bureau International des Poids et Mesures (https://www.bipm.org/en/publications/si-brochure)
- Calculated on this page — At One Place (/about/)