Centimeters to Millimeters Converter
Enter a length in centimeters and this converter gives you the equivalent in millimeters instantly. The reverse conversion works too: type in millimeters and read back centimeters. You also get the equivalent in metres, inches, and feet so you never need to switch tools. The formula, a worked example, and a reference table are included below.
Formula
Worked example
Convert 15 cm to mm: 15 x 10 = 150 mm. To reverse: 150 mm / 10 = 15 cm. The same length in other units: 15 cm = 0.15 m, 5.906 in, 0.492 ft.
How to convert cm to mm
The centimetre and the millimetre are both metric units of length. There are exactly 10 millimetres in 1 centimetre, so the conversion is a simple multiplication: mm = cm x 10. For example, 7.5 cm x 10 = 75 mm. To go the other way, divide by 10: cm = mm / 10. Both units sit on the same base-10 metric scale, so moving between them just shifts the decimal point one position.
When to use mm versus cm
Centimetres are common for everyday measurements such as body dimensions, furniture, and fabric. Millimetres are preferred in engineering, manufacturing, and carpentry, where precision below a centimetre matters: a machined part tolerance of 0.5 mm or a tile gap of 2 mm are typical examples. Scientific contexts often use millimetres or metres exclusively to avoid ambiguity. In medical imaging, lesion and organ measurements are nearly always recorded in millimetres.
Centimetres, millimetres and the metric system
Both units belong to the International System of Units (SI). The metre is the SI base unit of length (symbol m). A centimetre is one hundredth of a metre (prefix centi- means 10^-2), and a millimetre is one thousandth of a metre (prefix milli- means 10^-3). Because the system is decimal, all conversions between metric length units are exact powers of 10. There are 10 mm in 1 cm, 100 cm in 1 m, and 1000 mm in 1 m.
Converting to imperial units
One inch equals exactly 25.4 mm, which means 1 cm = 25.4 / 10 = 2.54 mm per tenth-inch, or more usefully 1 inch = 2.54 cm. To convert cm to inches, divide by 2.54 (equivalently multiply by 0.393701). To convert cm to feet, divide by 30.48 (multiply by 0.032808). This converter shows both imperial equivalents automatically so you can cross-check metric and imperial measurements in one step.
Centimeters to Millimeters conversion table
| Centimeters (cm) | Millimeters (mm) | Metres (m) | Inches (in) |
|---|---|---|---|
| 0.1 | 1 | 0.001 | 0.0394 |
| 0.5 | 5 | 0.005 | 0.1969 |
| 1 | 10 | 0.01 | 0.3937 |
| 2 | 20 | 0.02 | 0.7874 |
| 2.54 | 25.4 | 0.0254 | 1 |
| 5 | 50 | 0.05 | 1.9685 |
| 10 | 100 | 0.1 | 3.937 |
| 15 | 150 | 0.15 | 5.9055 |
| 20 | 200 | 0.2 | 7.874 |
| 25 | 250 | 0.25 | 9.8425 |
| 30 | 300 | 0.3 | 11.811 |
| 50 | 500 | 0.5 | 19.685 |
| 100 | 1000 | 1 | 39.37 |
Common centimetre values and their exact millimetre equivalents.
Frequently asked questions
How many mm in 1 cm?
There are exactly 10 millimetres in 1 centimetre. Because both are metric units based on powers of 10, the conversion is always a simple multiplication: mm = cm x 10.
How do I convert mm back to cm?
Divide the millimetre value by 10. For example, 85 mm / 10 = 8.5 cm. You can also type the mm value directly into this calculator in the input field, since the conversion is bidirectional.
What is 1 cm in mm?
1 centimetre equals exactly 10 millimetres. The formula is mm = 1 x 10 = 10 mm.
How many cm is 25.4 mm?
25.4 mm / 10 = 2.54 cm. This is a useful landmark value because 1 inch = 25.4 mm = 2.54 cm exactly, which makes it the bridge between the metric and imperial systems.
Why do engineers prefer millimetres over centimetres?
Millimetres allow tolerances and dimensions to be expressed as whole or near-whole numbers without decimal fractions as often as centimetres require. For instance, "30 mm" is cleaner than "3.0 cm" in a drawing, and "0.5 mm tolerance" is less ambiguous than "0.05 cm tolerance". Most international engineering standards, including ISO and DIN, specify dimensions in millimetres.
Is the cm to mm conversion exact?
Yes. 1 cm = 10 mm is a defined relationship within the SI metric system, not a rounded approximation. The conversion is always exact for any number of decimal places.