Inches to cm (in to cm)

One inch is exactly 2.54 centimeters. That is a definition rather than a measurement: the imperial and US customary units were fixed against metric ones by the 1959 international yard and pound agreement, so this factor does not drift and will not be revised.

Worked through: 20 in x 2.54 = 50.8 cm.

Going the other way, one centimeter is 0.3937007874 inches.

For mental arithmetic: Multiply by 2.5 and add 2%. 10 inches is 25 plus half a centimeter.

The reverse of the most-searched conversion there is, and the direction an American usually needs: reading a European product listing, a clothing size chart or a furniture dimension. Note that 2.54 is exact, so this is one of the few conversions where a repeating decimal never appears.

Precision is worth matching to the input. A measurement given as 1 in carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.