What it does
This converter changes a length between centimetres and inches, in either direction. Type a number and the answer appears as you type; the swap button flips which unit you are converting from. Nothing is sent to a server — the arithmetic runs in your browser.
How it works
There is one number to remember: 1 inch is exactly 2.54 centimetres. That is a definition, not a measurement — since 1959 the inch has been fixed at 2.54 cm by international agreement, so the conversion is exact and never rounds at source.
To go from centimetres to inches you divide by 2.54; to go the other way you multiply by 2.54. The two operations undo each other, which is why converting a value and then converting it back returns the number you started with.
Worked example
Take 2.54 cm. Dividing by the factor gives 2.54 ÷ 2.54 = 1, so 2.54 cm is exactly 1 inch. This is the cleanest case to picture, because 2.54 cm is the very length one inch is defined to be.
Exact factor, rounded output
The factor itself never rounds — but most conversions don't land on a tidy number, because dividing by 2.54 usually produces a repeating decimal. 30 cm works out to 11.8110236… in, which the tool displays rounded to four decimal places, as 11.811 in. Going the other way is exact whenever the input is a whole number of inches: 12 in (one foot) × 2.54 = 30.48 cm, with no rounding needed at all.
Common uses
- Height: reading a height given in centimetres on a passport or medical form when you think in feet and inches, or the reverse.
- Screen and TV sizes: screens are sold by their diagonal in inches, but fit into spaces measured in centimetres.
- Sewing, knitting and DIY: patterns and timber are often quoted in one unit while your tape measure reads the other.
- UK and US contexts: swapping between metric measurements and the inches still used for many everyday items on both sides of the Atlantic.
Frequently asked
How many centimetres are in an inch?
Exactly 2.54. One inch equals 2.54 cm, so ten inches is 25.4 cm and a foot (12 inches) is 30.48 cm.
Is 2.54 exact, or rounded?
It is exact. The inch is defined as 2.54 cm under the 1959 international yard and pound agreement, so there is no longer error in the figure — any rounding you see is only in how the answer is displayed.
How do I convert my height?
First turn your height into total inches, then multiply by 2.54. For example, 5 ft 9 in is (5 × 12) + 9 = 69 inches, and 69 × 2.54 = 175.26 cm. To go from centimetres back to feet and inches, divide by 2.54 to get inches, then split off whole feet.
Is there a difference between this and the US survey inch?
A tiny one, now retired. The old US survey foot, used for older land-survey and property records, was defined as 1200⁄3937 metres — very slightly longer than the international foot of exactly 0.3048 m, by about 2 parts per million. That made the survey inch fractionally longer than the international inch this converter uses. NIST retired the US survey foot on 1 January 2023, so current US federal measurements all use the international foot and inch — the same 2.54 cm this tool uses — and the distinction now only matters for historical survey data.
Why do some sources round an inch to 2.5 cm?
2.5 is a rough mental-maths shortcut, not the real figure — about 1.6% short of the true value. That's fine for a ballpark estimate but compounds over larger lengths: 100 × 2.5 = 250 cm, when the true figure for 100 inches is 254 cm. Use the exact 2.54 for anything you'll act on.
What about miles and kilometres?
Those are a different unit on a different scale — use the separate miles ⇄ kilometres converter. Our guide on why miles and kilometres often land close to round numbers covers the pattern if you're curious why that conversion feels tidier than this one.