Centimetres to Inches Converter
1 inch = 2.54 cm exactly. Type in either box.
—
Everything rests on 2.54
An inch is exactly 2.54 centimetres. Not approximately — exactly, by international agreement since 1959.
1 in = 2.54 cm exactly
Before that agreement the British and American inches differed very slightly, which was tolerable until wartime manufacturing required parts made in one country to fit those made in the other. The two-decimal figure was chosen to be exact and has not moved since.
Every other imperial length on this site descends from it. The foot is twelve of these inches, the yard thirty-six, the mile 63,360.
For mental work, dividing by 2.5 instead of 2.54 gives an answer about 1.6 % high — fine for judging whether furniture fits, not for cutting material.
The centimetre
A hundredth of a metre, and the unit of rulers, body measurements and packaging. It is not much used in engineering — drawings jump from millimetres to metres — but it is what most people reach for in everyday life.
Roughly, an inch is two and a half centimetres, which makes 2.54 one of the most useful numbers to memorise.
The inch
Defined since 1959 as exactly 2.54 centimetres. Before that Britain and America had slightly different inches, which caused real problems in wartime manufacturing and prompted the agreement that fixed it.
The inch survives in screen sizes, pipe diameters, tyre rims and paper measurements worldwide, even in countries that are otherwise entirely metric.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
How much is that?
A number is easier to judge next to something familiar.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where length conversions come up
- Height. Quoted in feet and inches in Britain and America, and in centimetres nearly everywhere else. 5 ft 10 in is 178 cm.
- Buying things online from another market, where the dimensions are in units your tape measure does not have.
- DIY and building, where materials come in metric sizes and older plans are in imperial.
- Screens, tyres and pipes, which stay in inches worldwide even in fully metric countries.
- Running and cycling, where race distances are metric and training apps may report either.
Numbers worth carrying
- 1 inch = 2.54 cm exactly. Everything imperial in this family descends from it.
- 1 foot = 30.48 cm, twelve inches.
- 1 yard = 0.9144 m, a little shorter than a metre.
- 1 mile = 1.609 km, and 1 km = 0.621 mile.
- A metre is about 39.37 inches, or 3 ft 3 in.
Mental shortcuts
Kilometres to miles: multiply by six and drop the last digit. 80 km × 6 = 480, drop the digit for 48 miles, against a true 49.7.
Miles to kilometres: add sixty per cent. 50 miles plus 60 % is 80 km, against a true 80.5.
Centimetres to inches: divide by 2.5 and take off a little. Dividing by 2.5 gives an answer about 1.6 % high.
Mistakes worth avoiding
- Feet and inches are not decimal. 5.5 feet is 5 ft 6 in, not 5 ft 5 in. Multiply the decimal part by twelve.
- Do not use length factors for area or volume. A foot is 0.3048 m, but a square foot is 0.0929 m² and a cubic foot 0.0283 m³.
- Check which mile. A nautical mile is 1,852 m, about 15 % longer than a statute mile.
Values people look up most
Each one opens the converter with the number already in it.
- 1 cm to in
- 2 cm to in
- 5 cm to in
- 10 cm to in
- 15 cm to in
- 20 cm to in
- 25 cm to in
- 30 cm to in
- 40 cm to in
- 50 cm to in
- 60 cm to in
- 70 cm to in
- 80 cm to in
- 90 cm to in
- 100 cm to in
- 120 cm to in
- 150 cm to in
- 160 cm to in
- 170 cm to in
- 180 cm to in
Quick reference
| Centimetres | Inches |
|---|---|
| 1 cm | 0.393701 in |
| 5 cm | 1.968504 in |
| 10 cm | 3.937008 in |
| 20 cm | 7.874016 in |
| 30 cm | 11.811024 in |
| 50 cm | 19.685039 in |
| 100 cm | 39.370079 in |
| 150 cm | 59.055118 in |
| 180 cm | 70.866142 in |
| 200 cm | 78.740157 in |
Questions people ask
What is the formula for cm to inches?
Divide by 2.54.
How many inches is 30 cm?
11.81 inches, just under a foot.
Is 2.54 exact?
Yes. The inch has been defined as exactly 2.54 cm since 1959.
What is 180 cm in feet and inches?
70.87 inches, which is 5 ft 10.9 in.