How to convert inches to cm
An inch is a US and imperial unit of length; a centimeter is one hundredth of a meter. The two are linked by one exact factor, so converting inches to centimeters is a single multiplication, whether the input is a clean number or a tape-measure fraction like 3/16.
The formula
2.54 is exact, not measured, because 1 inch is defined as exactly 25.4 mm, which is exactly 2.54 cm.
Worked example
74 in to centimeters:
74 × 2.54 = 187.96 cm, exactly, since the multiplication resolves to a finite decimal.
Fraction input: 1 1/4 in (1.25 in) to centimeters: 1.25 × 2.54 = 3.175 cm.
Reverse direction: 50 cm to inches: 50 ÷ 2.54 = 19.685 in.
Reference chart: inches to cm
| Inches | Centimeters |
|---|---|
| 1 in | 2.54 cm |
| 2 in | 5.08 cm |
| 3 in | 7.62 cm |
| 4 in | 10.16 cm |
| 5 in | 12.7 cm |
| 6 in | 15.24 cm |
| 7 in | 17.78 cm |
| 8 in | 20.32 cm |
| 9 in | 22.86 cm |
| 10 in | 25.4 cm |
| 11 in | 27.94 cm |
| 12 in | 30.48 cm |
| 18 in | 45.72 cm |
| 24 in | 60.96 cm |
| 30 in | 76.2 cm |
| 36 in | 91.44 cm |
| 42 in | 106.68 cm |
| 48 in | 121.92 cm |
| 54 in | 137.16 cm |
| 60 in | 152.4 cm |
| 66 in | 167.64 cm |
| 72 in | 182.88 cm |
The exact factor: why 1 inch is exactly 2.54 cm
Before July 1, 1959, the US inch and the UK (imperial) inch were not identical: each country used its own legal definition, differing from the other by roughly two parts per million, a few millionths of an inch. The International Yard and Pound Agreement, signed by the United States, the United Kingdom, Australia, Canada, New Zealand, and South Africa, fixed the international yard at exactly 0.9144 meters, which fixes the inch at exactly 25.4 mm, or exactly 2.54 cm, everywhere those countries use it.
When precision matters: woodworking vs machining
If you are cutting a board to a plan given in centimeters, rounding your inches figure to the nearest 16th on a tape measure costs you a fraction of a millimeter, which almost never matters for framing, shelving, or furniture. If you are machining a part or 3D printing to a metric tolerance, that same 16th-inch rounding can be worth 1.5 mm or more, which is too coarse for a fitted joint or a bearing seat. When the target hardware is metric, it is usually cleanest to work entirely in millimeters or centimeters and skip the inch conversion altogether.
Related conversions
Prefer millimeters? Try the MM to Inches Converter. Starting from centimeters as your primary input? See the CM to Inches Converter. Need feet instead of a fraction? Use the Inches to Feet Converter. Converting a person's height, see the Height Converter, or for meters and feet see the Meters to Feet Converter.