How this works
1 inch = 2.54 cm exactly. The conversion has been an exact, defined value since the 1959 international yard-and-pound agreement — there's no approximation involved when going from inches to centimetres. Type an inch value above and the converter shows the exact centimetre figure plus every other common length unit.
The formula
For mental conversion, multiply by 2.5 for a quick approximation (off by 1.6%) — e.g. 12 in × 2.5 ≈ 30 cm (actual: 30.48). For combined feet-and-inches, convert each separately and add: 5 ft 9 in = (5 × 12 + 9) × 2.54 = 69 × 2.54 ≈ 175 cm.
Example calculation
- 1 in = 2.54 cm
- 6 in = 15.24 cm
- 12 in = 30.48 cm (1 foot)
- 69 in = 175.26 cm (5 ft 9 in, average male height)
Frequently asked questions
How do I convert feet and inches to cm in one step?
Multiply feet by 12 to get total inches, add the inch part, then multiply by 2.54. For 5 ft 9 in: (5 × 12 + 9) × 2.54 = 69 × 2.54 = 175.26 cm. The all-pairs Length Converter handles any pair of units in one go if you'd rather not do the arithmetic by hand.
Why does the calculator show the same number with lots of decimals?
For inches it doesn't — 1 in = 2.54 cm exactly, so the conversion is finite. But other targets (e.g. yards, feet) involve factors that aren't round in the metric base, so you'll see more digits. Round to 1-2 decimal places for everyday use; keep all of them for engineering or precision-critical work.