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Inches to CM

Type in either box. Instant, exact, and it works offline.

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Convert a length

Conversion values

Centimetrescm

30.48
Units and precision
1 in = 2.54 cm exactly

How it works

  1. 01

    Type a length

    Plain numbers, decimals, or tape-measure fractions like 3 1/2. The answer updates as you type.

  2. 02

    Pick the units

    Pick any unit from millimetres to miles on either side. The swap button reverses the conversion and carries the answer across.

  3. 03

    Choose the precision

    Up to ten decimal places. The factor is exact, so rounding only happens where you ask for it.

Conversion table

Common inch measurements and their exact centimetre equivalents
InchesCentimetresInchesCentimetres
1/80.321025.40
1/40.641230.48
1/21.271845.72
12.542460.96
25.083691.44
615.2460152.40

Where the number comes from

The inch has been exactly 25.4 millimetres since the 1959 international yard and pound agreement. So this conversion is exact. Multiply by 2.54 to get centimetres, and divide by 2.54 to go back. The only rounding comes from the number of decimal places you choose.

Older definitions still turn up in technical documents. One is the US survey inch, which land surveyors used until 2022. It was about 2 parts per million longer. That is far too small to see on a desk, but it adds up to about 3 mm across a mile of survey line.

Exact factor
1 in = 2.54 cm = 25.4 mm
Reverse
1 cm = 0.393701 in
Rounding
Up to 10 decimal places, your choice.
Other units
The From and To lists cover mm, m, ft, yd and more.

Frequently asked questions

How many centimetres are in an inch?
Exactly 2.54. The relationship is defined, not measured, so the factor holds no rounding error. The only rounding is in how many decimal places you display.
Can I convert centimetres back to inches here?
Yes. Choose Centimetre in the From field and Inch in the To field, or press the swap button between the two boxes.
Does it handle fractions like 3 1/2?
Yes. Common fractions and mixed numbers both work. So 1/8, 3 1/2 and -2 1/4 all convert as you would read them off a tape.
How precise is the result?
You can display up to 10 decimal places. The calculation uses the exact 2.54 conversion factor before formatting the result.
Is there a limit on conversions?
No. Conversions run locally in your browser and have no daily or account limit.
Does this work without an internet connection?
Yes. Once the page has loaded, the calculation runs entirely on your device without sending the number anywhere.

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