Each centimetre is 10 millimetres, so multiply by 10. Rulers mark both: the long lines are centimetres and the small ones millimetres.
How to use the cm to mm Converter
- Type the number of centimetres into the Centimetres field. Decimals such as 1.25 are fine.
- Read the answer in Millimetres – it updates as you type, with no button to press.
- To convert the other way, type into Millimetres and the centimetres are recalculated.
- Press Copy results to copy both values with the page title, or Copy link to share this exact conversion.
This page converts only cm ⇄ mm. Need a different unit? Use the general length converter, where you can choose any “from” and “to” unit.
How it works
Both units measure length, so they are always in the same ratio: one centimetre equals 10 millimetres. The calculator multiplies the number of centimetres you type by 10 to give millimetres, and when you type into the millimetres field it divides by the same factor to give centimetres. Because the ratio never changes, doubling the centimetres always doubles the millimetres. Results are calculated at full precision and rounded only for display (up to eight decimal places, with very large or small values shown in scientific notation).
How to convert centimetres to millimetres
- Write down the value in centimetres, for example 2.5 cm.
- Multiply by the conversion factor 10 (because 1 centimetre = 10 mm).
- 2.5 × 10 = 25 mm.
- To go back from millimetres to centimetres, divide by 10 – or multiply by 0.1.
cm to mm conversion table
| Centimetres | Millimetres | Millimetres | Centimetres |
|---|---|---|---|
| 0.1 cm | 1 mm | 1 mm | 0.1 cm |
| 0.5 cm | 5 mm | 2 mm | 0.2 cm |
| 1 cm | 10 mm | 5 mm | 0.5 cm |
| 2 cm | 20 mm | 10 mm | 1 cm |
| 2.5 cm | 25 mm | 20 mm | 2 cm |
| 3 cm | 30 mm | 50 mm | 5 cm |
| 5 cm | 50 mm | 100 mm | 10 cm |
| 10 cm | 100 mm | 1,000 mm | 100 cm |
| 15 cm | 150 mm | ||
| 30 cm | 300 mm | ||
| 50 cm | 500 mm | ||
| 100 cm | 1,000 mm |
What is a centimetre?
A centimetre is one hundredth of a metre (10 mm). It is the everyday metric unit for body height, clothing, furniture and school rulers.
What is a millimetre?
A millimetre is one thousandth of a metre. Engineering drawings, construction plans, rainfall, screws, bolts and jewellery are all dimensioned in millimetres.
Common mistakes to avoid
Mixing the international foot (0.3048 m) with the old u.s. survey foot, confusing nautical and statute miles, and writing decimal feet such as 5.5 ft as “5 ft 5 in” (it is 5 ft 6 in).
Formula
1 cm = 10 mm1 mm = 0.1 cmmm = cm × 10Worked example
Inputs — Centimetres: 2.5 cm.
Results — Millimetres = 25 mm.
Frequently asked questions
How many mm in 2.5 cm?
25 mm.
How many mm in an inch?
25.4 mm.
How do I convert centimetres to millimetres?
Multiply the number of centimetres by 10. For example, 2.5 cm × 10 = 25 mm.
How do I convert millimetres back to centimetres?
Divide by 10 (or multiply by 0.1), or simply type the value into the millimetres field above.
What is 10 cm in millimetres?
10 cm = 100 mm.
What is 100 cm in millimetres?
100 cm = 1,000 mm.
Is this conversion exact?
Yes. The factor comes from the official definitions of both units (NIST and the SI), so the only difference you may see is rounding in the last displayed digit.
Can I convert to other units on this page?
This page converts only between centimetres and millimetres. To pick any length unit, use the general length converter linked under Related calculators.
What formula does the cm to mm Converter use?
1 cm = 10 mm.