Inch to cm Converter

One inch is exactly 2.54 centimetres. That word, exactly, is doing real work: the factor is a definition, not a measurement, so it carries no rounding error at any number of decimal places.

Before 1959 the inch differed slightly between countries, and a US inch was not quite a British inch. The international yard and pound agreement fixed the yard at exactly 0.9144 metres, which makes the inch exactly 0.0254 metres, and the discrepancy disappeared.

Going the other way, one centimetre is 0.3937007874 inches. That figure does repeat forever, because it is the reciprocal of an exact number rather than a defined one.

1 inch is 2.54 cm. 2 inches is 5.08 cm. 5 inches is 12.7 cm. 10 inches is 25.4 cm.

12 inches, one foot, is 30.48 cm. 24 inches is 60.96 cm. 36 inches, one yard, is 91.44 cm.

For a rough estimate without a calculator, multiply by 2.5 and add a bit: 10 inches is a little over 25 cm, and 40 inches is a little over 100 cm.

Screen sizes are quoted as the diagonal in inches, so a 27 inch monitor measures 68.58 cm corner to corner. Wheel and rim diameters, bicycle frames, and pipe threads follow the same pattern.

In each case the inch figure is a product name as much as a measurement, which is why it survives in countries that otherwise use the metric system throughout.