The CM to Inches Calculator converts centimetres to inches by dividing by 2.54, the exact number of centimetres in one inch, and converts back the other way by multiplying. Enter a value in either field and the result appears instantly, alongside the factor used, the working, and a table of common conversions.
The conversion is exact, not approximate. One inch has equalled 2.54 centimetres by international agreement since 1959, so every cm-to-inches result is a precise figure rather than a rounded estimate.
Convert centimetres to inches
Converting centimetres to inches takes one step: divide the number of centimetres by 2.54. That single factor handles every cm-to-inches conversion, because an inch is defined as exactly 2.54 centimetres. Enter a centimetre value and the CM to Inches Calculator returns the inches immediately.
The conversion runs live as you type, so there is no button to press, and the reverse direction works the same way, type into the inches field to get centimetres.
The result carries full precision and rounds only for display, with a control to set how many decimal places you want. For most everyday purposes two decimal places is plenty; for engineering or tailoring you may want more.
Apply the cm to inches factor
The cm to inches factor is exactly 2.54 centimetres per inch, which means the conversion is a simple division:
inches = centimetres ÷ 2.54Because the factor is exact, the only rounding in the whole calculation happens when the result is displayed. A conversion of 30 cm gives 11.811 inches, and that figure is precise to as many decimal places as you care to show.
The factor comes from the international yard and pound agreement of 1959, when the United States, United Kingdom, Canada, Australia, New Zealand and South Africa fixed the inch at exactly 2.54 centimetres. Before that, the inch varied slightly between countries; since then it has been identical everywhere.
Convert inches to centimetres
Converting inches to centimetres reverses the operation: multiply the number of inches by 2.54.
centimetres = inches × 2.54So 10 inches is 10 × 2.54 = 25.4 centimetres, exactly. The CM to Inches Calculator handles this direction with the same swap control, press it, or simply type into the inches field, and the calculator converts to centimetres instead. A converter has no fixed direction, and this one works both ways from a single tool.
Convert 20 cm to inches
Take a worked example: converting 20 centimetres to inches. 1. State the factor. 1 inch = 2.54 cm, exactly. 2. Divide. 20 ÷ 2.54 = 7.874 inches. So 20 centimetres equals 7.874 inches, or close to 7⅞ inches for practical purposes.
The calculator shows this working under every result, so the conversion is transparent rather than a number appearing from nowhere, useful when you need to show the method or check it by hand.
For a quick mental estimate, dividing by 2.5 instead of 2.54 gets you close: 20 ÷ 2.5 = 8, within about 2% of the true answer. That shortcut is handy when an exact figure is not needed.
Read the cm to inches table
The CM to Inches Calculator shows a reference table of common centimetre values and their inch equivalents, centred on the value entered. The table is the fastest way to look up a conversion without typing, and it is what makes these pages worth bookmarking.
| Centimetres | Inches |
|---|---|
| 1 | 0.394 |
| 5 | 1.969 |
| 10 | 3.937 |
| 15 | 5.906 |
| 20 | 7.874 |
| 25 | 9.843 |
| 30 | 11.811 |
| 50 | 19.685 |
| 100 | 39.370 |
Each row is generated from the exact factor, so the table is as precise as the calculator itself. Clicking any row loads that value into the converter.
Convert to fractional inches
Inches are often measured in fractions rather than decimals, especially in woodworking, tailoring and construction, so the CM to Inches Calculator also gives the result as a fraction to the nearest sixteenth. A decimal like 7.874 inches becomes 7⅞ inches to the nearest eighth, or 7¹⁴⁄₁₆ before simplifying.
For practical measuring against a ruler or tape marked in fractions, the fractional form is what you actually use, and the decimal form is only an intermediate step.
The calculator rounds to the nearest sixteenth by default, which matches most tape measures, and shows both the decimal and the fraction so you can pick whichever suits the task.
Frequently asked questions
How do I convert cm to inches?
To convert centimetres to inches, divide the number of centimetres by 2.54, since one inch equals exactly 2.54 centimetres. For example, 20 cm ÷ 2.54 = 7.874 inches. The CM to Inches Calculator does this instantly and shows the working, and it converts back to centimetres by multiplying inches by 2.54.
How many inches is 1 cm?
One centimetre equals 0.3937 inches, found by dividing 1 by 2.54. That is a little under four tenths of an inch. The figure is exact to as many decimal places as needed, because the inch is defined as exactly 2.54 centimetres, making every cm-to-inches conversion precise rather than approximate.
Is the cm to inches conversion exact?
Yes. The inch has been defined as exactly 2.54 centimetres by international agreement since 1959, so converting between them introduces no approximation. Any rounding you see is only in the displayed result, not in the conversion itself. A value of 20 cm is exactly 7.874015... inches, shown to whatever precision you choose.
How do I convert inches back to cm?
To convert inches to centimetres, multiply the number of inches by 2.54. For example, 10 inches × 2.54 = 25.4 centimetres, exactly. The CM to Inches Calculator reverses direction with its swap control, or you can simply type into the inches field to convert the other way, since a converter works in both directions from one tool.
What is 20 cm in inches?
20 centimetres equals 7.874 inches, calculated as 20 ÷ 2.54. For practical purposes that rounds to about 7⅞ inches on a fractional tape measure. The CM to Inches Calculator shows both the exact decimal and the nearest fraction, so the result works whether you need a precise figure or a measurement you can mark on a ruler.
Why is one inch 2.54 cm?
One inch equals 2.54 centimetres because the international yard and pound agreement of 1959 fixed it at that exact value, standardising the inch across the English-speaking countries that had previously used slightly different definitions. The round 2.54 figure was chosen to tie the imperial inch cleanly to the metric system, and it has been the definition everywhere since.
How do I estimate cm to inches without a calculator?
For a rough estimate, divide the centimetres by 2.5 instead of 2.54, which is easy to do mentally and lands within about 2% of the exact answer. For example, 20 ÷ 2.5 = 8 inches, close to the true 7.874. When precision matters, use the exact 2.54 factor, but the shortcut is fine for a quick sense of the size.
Summary
The CM to Inches Calculator converts centimetres to inches by dividing by 2.54, and inches to centimetres by multiplying by the same figure, since one inch is defined as exactly 2.54 centimetres. The conversion is precise rather than approximate, a definition fixed by international agreement in 1959, so the only rounding occurs when the result is displayed.
The calculator works in both directions from a single tool, shows the factor and the working under every result, gives the answer as a fraction to the nearest sixteenth for practical measuring, and lists a table of common cm-to-inch values for quick reference. For a rough mental estimate, dividing by 2.5 lands within about 2% of the exact answer.