To convert centimetres to inches, divide the number of centimetres by 2.54. To go the other way, multiply inches by 2.54. So 30 cm is 30 ÷ 2.54 = about 11.8 inches. The length converter does it instantly and shows your value in every other unit too.
That is the whole rule. Here is a little more on why it works and how to estimate in your head.
Why 2.54 is exact
Since 1959, an inch has been defined as exactly 2.54 centimetres by international agreement. It is not an approximation that happens to be close; it is the definition. That means cm-to-inch conversions are perfectly precise, and any rounding you see is only for display. One inch is 25.4 millimetres, one foot is 30.48 centimetres, and one yard is 91.44 centimetres, all derived from that single factor.
How to convert cm to inches
Convert centimetres to inches
Divide by 2.54.
- 10 cm ÷ 2.54 = 3.94 inches
- 100 cm ÷ 2.54 = 39.37 inches
Convert inches to centimetres
Multiply by 2.54.
- 6 in × 2.54 = 15.24 cm
- 12 in × 2.54 = 30.48 cm
The length converter handles both directions, so you can type in whichever unit you have and read the other.
A quick mental shortcut
When you only need a rough figure, divide centimetres by 2.5 instead of 2.54. It is close enough for everyday use and easy to do in your head: halve the number, then halve again, then… actually, simplest is to divide by 2.5 directly, so 50 cm is about 20 inches. The true answer is 19.69, so the shortcut runs slightly high, but for picturing a size it is fine.
Where it matters
Getting this right matters most when small errors add up or when a fit is involved:
- Screens and TVs, which are measured diagonally in inches almost everywhere.
- Height, often given in feet and inches in some countries and centimetres in others.
- DIY and crafts, where a plan in one system and a tape measure in the other is a recipe for mistakes.
- Clothing and shoes, where size charts mix the two.
For any of these, use the exact factor rather than the estimate. To convert weights the same way, see the weight converter, or browse every unit on the length converter.