Free metric converter
Cm to Mm Conversion Calculator
Convert centimeters (cm) to millimeters (mm) and back in real time. The metric relationship is exact: 1 cm = 10 mm. Type a value in either box; the other updates instantly.
Quick conversion table
| Centimeters (cm) | Millimeters (mm) |
|---|---|
| 0.1 | 1 |
| 0.5 | 5 |
| 1 | 10 |
| 5 | 50 |
| 10 | 100 |
| 25 | 250 |
| 50 | 500 |
| 100 | 1000 |
Formulas
Worked example: 25 cm × 10 = 250 mm. Reverse: 300 mm ÷ 10 = 30 cm.
When to use cm vs mm
Use millimeters (mm)
- Engineering drawings, machining tolerances, and CAD
- Print design: crop marks, bleed, and hairline specs
- Small measurements where precision matters (e.g. 0.5 cm = 5 mm is easier to read on a steel ruler than 0.5 cm)
Use centimeters (cm)
- Everyday lengths: body measurements, clothing sizes, furniture
- School math problems and general measurements
- When 1 mm precision is unnecessary (e.g. 150 cm tall)
Centimeters to millimeters explained
The centimeter and millimeter are both SI metric units of length. "Milli" means one-thousandth of a meter and "centi" means one-hundredth, so one centimeter contains exactly ten millimeters. This ratio is exact by definition, not a measured value, so converting cm to mm never loses precision: multiply by 10.
Common conversions people look up: 1 inch = 2.54 cm = 25.4 mm, a credit card (8.5 cm) is 85 mm long, and a 150 cm person is 1500 mm tall.
This free cm to mm calculator runs entirely in your browser. No sign-up, no server, no tracking of your numbers.
Frequently asked questions
How many millimeters are in 1 centimeter?
Exactly 10. One centimeter equals 10 millimeters: 1 cm = 10 mm. Multiply any centimeter value by 10 to get millimeters.
How do you convert cm to mm?
Multiply centimeters by 10. For example, 5.5 cm × 10 = 55 mm, and 0.5 cm × 10 = 5 mm.
How do you convert mm to cm?
Divide millimeters by 10. For example, 25 mm ÷ 10 = 2.5 cm, and 300 mm ÷ 10 = 30 cm.
Is 10 mm the same as 1 cm?
Yes, exactly. 10 mm = 1 cm is an exact metric definition, so there is no rounding involved.
How many mm is 2.54 cm?
25.4 mm. Since 2.54 cm equals 1 inch, one inch is exactly 25.4 millimeters.
How many mm is 25 cm?
250 mm. Multiply: 25 × 10 = 250.
What is 0.5 cm in mm?
5 mm. Half a centimeter equals five millimeters.
What is the formula for cm to mm conversion?
mm = cm × 10. To go the other way, cm = mm ÷ 10.
Why do engineers use mm instead of cm?
Millimeters avoid decimals for small features. Writing 5 mm is cleaner than 0.5 cm on engineering drawings, and tolerances in mm are less error-prone to read and machine.
Which is bigger, cm or mm?
The centimeter is bigger: 1 cm = 10 mm, so one millimeter is one-tenth of a centimeter (1 mm = 0.1 cm).
How many mm are in 150 cm?
1500 mm. Multiply: 150 × 10 = 1500.
Is this cm to mm calculator free and private?
Yes. It is free, works offline once loaded, and every conversion happens on your device, so no measurement data leaves your browser.
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