How to convert inches to cm
Since 1959 an inch has been defined as exactly 2.54 centimetres, so the conversion is a single multiplication with no rounding involved. Multiply inches by 2.54 to get centimetres, or by 25.4 to get millimetres.
cm = inches × 2.54
mm = inches × 25.4
inches = cm ÷ 2.54
If you've got feet as well, turn them into inches first: there are 12 inches in a foot, so 2 ft 6 in is 30 inches, which is 76.2 cm.
For a rough figure in your head, 4 inches is just over 10 cm, and 1 cm is about 0.4 of an inch.
Worked examples
How many cm is 12 inches?
12 × 2.54 = 30.48 cm. A foot ruler is 30.48 cm long, which is why most school rulers show 30 cm on one edge and 12 inches on the other.
What is 5 3/8 inches in mm?
3/8 is 0.375, so 5 3/8 in is 5.375 in. Then 5.375 × 25.4 = 136.5 mm. Pick 3/8 from the fraction box and the calculator does this for you, which is handy for drill bits, spanners and timber sizes still sold in imperial.
What is 75 cm in inches?
75 ÷ 2.54 = 29.53 in, or just over 29 1/2 inches. In feet and inches that's 2 ft 5.5 in.
Common sizes in inches and cm
TV and monitor screens
Screen sizes are measured corner to corner (diagonally), not across the width.
| Screen size | Diagonal in cm |
|---|---|
| 24 in | 61.0 cm |
| 32 in | 81.3 cm |
| 43 in | 109.2 cm |
| 50 in | 127.0 cm |
| 55 in | 139.7 cm |
| 65 in | 165.1 cm |
| 75 in | 190.5 cm |
Waist and inside leg sizes
| Inches | Centimetres |
|---|---|
| 28 in | 71.1 cm |
| 30 in | 76.2 cm |
| 32 in | 81.3 cm |
| 34 in | 86.4 cm |
| 36 in | 91.4 cm |
| 38 in | 96.5 cm |
| 40 in | 101.6 cm |
Fractions of an inch in mm
| Fraction | Decimal inches | Millimetres |
|---|---|---|
| 1/16 in | 0.0625 | 1.6 mm |
| 1/8 in | 0.125 | 3.2 mm |
| 1/4 in | 0.25 | 6.4 mm |
| 3/8 in | 0.375 | 9.5 mm |
| 1/2 in | 0.5 | 12.7 mm |
| 5/8 in | 0.625 | 15.9 mm |
| 3/4 in | 0.75 | 19.1 mm |
| 7/8 in | 0.875 | 22.2 mm |
Tips
- Measuring your height? Use the cm to feet calculator, which gives height in feet and inches.
- Working out a floor or wall? The square metre calculator converts room sizes to m² and square feet.
- Buying timber or plasterboard? UK sheet materials are sold in metric sizes that started life as imperial: a standard 2400 × 1200 mm sheet is close to 8 ft × 4 ft but slightly smaller (8 ft × 4 ft is 2438 × 1219 mm).
- Copper pipe sizes such as 15 mm and 22 mm replaced 1/2 inch and 3/4 inch pipe, but the old and new sizes don't match exactly, so you need adaptors to join them.
Frequently asked questions
How many cm is 1 inch?
One inch is exactly 2.54 cm, which is 25.4 mm.
How do I convert inches to cm?
Multiply the number of inches by 2.54. For example, 10 inches × 2.54 = 25.4 cm.
How many inches is 1 cm?
One centimetre is about 0.394 inches, so roughly 0.4 of an inch.
What is 30 cm in inches?
30 cm is 11.81 inches, just under a foot. A foot (12 inches) is 30.48 cm.
How big is a 55 inch TV in cm?
A 55 inch TV measures 139.7 cm corner to corner. TV sizes are always measured diagonally across the screen.
Last reviewed October 2026. Conversions use the exact international inch (2.54 cm).