Inches to Centimeters

Even in countries that went metric decades ago, a few product categories never left the inch. Television and monitor sizes are the obvious one: a 55-inch TV has a diagonal of 139.7 cm, and a 13-inch laptop screen measures 33.02 cm corner to corner. Jeans are sold by waist and inseam in inches almost everywhere, so a W32 L30 pair means an 81.28 cm waist and a 76.2 cm inseam. Bicycle wheels, car rims, pipe threads and the quarter-inch tripod screw on every camera are inch sizes too.

Photo prints follow the same pattern. A 4 × 6 in print is 10.16 × 15.24 cm, and US Letter paper is 8.5 × 11 in, or 21.59 × 27.94 cm, which is wider and shorter than A4. If you need an image to print at a physical size, the pixel converter turns inches into pixels at a chosen DPI, and you can resize an image in centimeters once you know the target.

Before 1959 the American inch was defined through a ratio to the meter that made it about 2.540005 cm, while the British inch was a hair shorter. The international yard and pound agreement of that year set the yard at exactly 0.9144 m, and since 36 inches make a yard, the inch became exactly 2.54 cm. The meter itself has been defined by the speed of light since 1983, so the inch now rests on a physical constant as well.

That makes this direction of the conversion clean: multiplying by 2.54 never produces an endless decimal. The rounding only shows up if you go the other way, from centimeters back to inches, which is covered on the centimeters to inches page.

Tape measures in the US are marked in halves, quarters, eighths and sixteenths, so turn the fraction into a decimal first: 3 5/8 in is 3.625 in, which is 9.2075 cm. A sixteenth of an inch is 1.5875 mm, a useful number to remember when a metric drill bit has to replace an imperial one.

For heights, convert everything to inches before multiplying. 5 ft 9 in is 69 in, and 69 × 2.54 gives 175.26 cm. Multiplying 5.9 by 30.48 gives 179.8 cm, which is wrong, because 5 ft 9 in is not 5.9 feet.