CM to Inches Converter
Type centimeters to get inches, with the nearest sixteenth of an inch for reading a tape measure.
30 cm =
11.811in
30 centimeters is 11.811 inches.
- Nearest 1/16 inch
- 11 13/16 in
- 1 cm
- 0.3937 in
- 1 in
- 2.54 cm
How this works: Method, 4 sources, Checked against 2 worked examples,
How this works
Method
Divide the number of centimeters by 2.54. The inch has been defined as exactly 2.54 cm since the international yard and pound agreement of 1959, so dividing by 2.54 gives the true answer, not an approximation. Full method
Sources
How it’s tested
2 worked examples for this page are checked by automated tests before every release: given the inputs, the tool must show the expected answer.
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Changes
- Ask understands “5 ft 9 in to cm” and “2 cups of flour in grams” and answers at once, and a decimal comma (“2,5”) reads as 2.5.
- First published: 89 everyday units across ten quantities, with 58 pages for common pairs such as cm to inches and Celsius to Fahrenheit.
How to convert cm to inches
Divide the number of centimeters by 2.54. The inch has been defined as exactly 2.54 cm since the international yard and pound agreement of 1959, so dividing by 2.54 gives the true answer, not an approximation.
For a 21 cm sheet of A4 paper: 21 ÷ 2.54 = 8.268 inches, a little narrower than US Letter at 8.5 inches. For a 42 cm suitcase depth: 42 ÷ 2.54 = 16.54 inches.
Tape measures in the US are marked in fractions, not decimals. To turn the decimal part into sixteenths, multiply it by 16 and round: 0.268 × 16 = 4.3, so 8.268 inches is about 8 4/16, which reduces to 8 1/4 inches.
inches = centimeters ÷ 2.54 (≈ centimeters × 0.393701)
- One inch is exactly 0.0254 m, so 1 cm is 1 ÷ 2.54 = 0.393700787… inches, a decimal that never ends. Source: NIST, SI units: length.
How to estimate cm to inches in your head
Multiply by 4 and drop a zero (that is, take 40%), then nudge the answer down a little. 30 cm × 0.4 = 12, and the true answer is 11.81, so “a bit under 12 inches” is right. Taking 40% is about 1.6% high, which is less than a sixteenth of an inch on anything shorter than 10 cm.
Another anchor: 10 cm is just under 4 inches (3.94), and 1 meter is just over 39 inches (39.37). A ruler marked 30 cm on one edge is 11.8 inches on the other, which is why a “12-inch” ruler is a few millimeters longer than a 30 cm one.
Centimeters to inches chart
Everyday lengths from a fingernail to a meter, with the inch value to three decimals.
| Centimeters (cm) | Inches (in) | Example |
|---|---|---|
| 1 | 0.3937 | about a fingernail’s width |
| 2 | 0.7874 | |
| 2.5 | 0.9843 | |
| 5 | 1.9685 | |
| 7.5 | 2.9528 | |
| 10 | 3.937 | |
| 12 | 4.7244 | |
| 15 | 5.9055 | |
| 20 | 7.874 | |
| 21 | 8.2677 | width of A4 paper |
Show all 23 rowsShow fewer
| 25 | 9.8425 | |
| 29.7 | 11.6929 | height of A4 paper |
| 30 | 11.811 | a school ruler |
| 35 | 13.7795 | |
| 40 | 15.748 | |
| 45 | 17.7165 | |
| 50 | 19.685 | |
| 60 | 23.622 | |
| 70 | 27.5591 | |
| 75 | 29.5276 | |
| 80 | 31.4961 | |
| 90 | 35.4331 | |
| 100 | 39.3701 | one meter |
Frequently Asked Questions
How many inches is 30 cm?
30 cm is 11.81 inches (30 ÷ 2.54). On a tape measure that is a hair under 11 13/16 inches, so a 30 cm ruler is about 3/16 inch short of a foot.
Is 2.54 exact or rounded?
Exact. Since 1959 the inch has been defined as 25.4 millimeters, so 1 inch = 2.54 cm with no rounding. The reverse factor, 0.3937, is the rounded one.
How do I convert cm to inches for a screen or TV size?
Screens are measured on the diagonal. Divide the diagonal in centimeters by 2.54: a 140 cm diagonal is 55.1 inches, sold as a 55-inch TV. Width and height convert the same way.