What this calculator does
Turn centimeters into inches, or inches into centimeters, in one step. A centimeter is one hundredth of a meter. It's the metric unit on school rulers, clothing tags and furniture listings in most of the world. An inch is the small unit used in the US and the older British system. The US uses it for almost every everyday measurement. Around the world, it's also used for screen sizes, wheel rims and pipe threads.
The two units are tied by an exact rule: one inch is 2.54 centimeters, no more and no less. That makes this one of the cleanest conversions there is. To go from inches to centimeters, multiply by 2.54. To go from centimeters to inches, divide by 2.54. Along with the decimal answer, you get the nearest 1/16 inch, the way you'd read a tape measure. You also get feet and inches for anything a foot or longer, and a chart from 1 to 200 cm.
Where it's used
Why this math matters outside the classroom:
- Screen sizes. A 55 in TV measures about 139.7 cm across its diagonal.
- Clothing. A waist measurement of 81 cm is about 31.9 in.
- Sewing. A pattern calling for a 1.5 cm seam allowance is just under 5/8 in, which is 1.5875 cm.
- Luggage. An airline cabin-bag limit of 55 cm is about 21.7 in.
- Tape measures. Students read both edges of a tape measure to see that 10 in lines up with 25.4 cm.
Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Type the length. Enter parts of an inch as decimals, for example 3/8 in as 0.375.
- Pick the direction: centimeters to inches, or inches to centimeters.
- Read the decimal answer and the tape-measure fraction. For longer lengths, such as a height, you'll also see feet and inches.
- Open the chart under the result to look up nearby sizes without retyping. The inches chart lists common fractions from 1/16 in.
What the inputs mean
- Value to convert
- A length in centimeters (cm → in) or inches (in → cm). Zero and decimals are fine.
- Direction
- Choose which unit you're starting from. The chart below changes to match.
Formula and method
in = cm ÷ 2.54 ≈ cm × 0.393700787402 cm = in × 2.54 nearest 1/16 in = round(in × 16) ÷ 16 feet = whole part of (in ÷ 12); inches left = in − 12 × feet
In the formulas, cm is the length in centimeters and in is the length in inches. "round" means round to the nearest whole number, and ≈ means "about equal to".
A 1959 international agreement set the inch at exactly 25.4 millimeters, which is 2.54 centimeters. That number has an end, so turning inches into centimeters never needs rounding.
Going from centimeters to inches means dividing by 2.54. You could multiply by 1 ÷ 2.54 instead, but that number (0.3937007874…) never ends. So the calculator divides, rather than multiplying by a rounded number.
US tape measures are marked in sixteenths of an inch. So the answer is also rounded to the nearest 1/16 and shown in its simplest form (8/16 shows as 1/2). That rounding is off by at most 1/32 in, less than 0.8 mm.
Worked example
A 30 cm ruler: how long is it in inches?
- Divide by the exact factor: 30 ÷ 2.54 = 11.811023622…
- For a tape-measure reading: 11.811 × 16 = 188.98, which rounds to 189 sixteenths, or 11 13/16 in.
Result: 30 cm is about 11.81 in (11 13/16 in on a tape). That's a little short of a 12-inch ruler, which is 30.48 cm.
Understanding the result
Here's a quick mental shortcut for cm to inches: multiply by 4, then divide by 10. For 30 cm that gives 12 in, while the exact answer is 11.81. That's about 1.6% too high.
For inches to cm, multiply by 2.5 and add a little. So 10 in gives about 25, and the exact answer is 25.4.
Some everyday sizes: a 15.6-inch laptop screen is 39.624 cm corner to corner, and a 32-inch TV is 81.28 cm. A person 5 ft 10 in tall (70 in) is 177.8 cm. And 180 cm is about 70.87 in, just under 5 ft 11 in. A sheet of US Letter paper, 8.5 × 11 in, is 21.59 × 27.94 cm.
Watch out: a screen's size in inches is measured corner to corner, not across. So 55 in becomes 139.7 cm corner to corner. The width is smaller, and it depends on the screen's shape.
Assumptions and limitations
- The inch is the international inch, exactly 2.54 cm.
- Values are lengths along a straight line, not areas or volumes.
- The tape-measure fraction is rounded to the nearest 1/16 in. For machining or anything finer, use the decimal answer.
- In feet and inches, the inches are rounded to one decimal place.
- Square inches and square centimeters need the factor squared (6.4516). Use the area converter for those.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54. It's a definition, not a measurement, so better tools will never change it.
How many inches is 1 cm?
About 0.3937 in, a little under 4/10 of an inch. Ten centimeters is roughly 3.94 in.
How do I convert my height in centimeters to feet and inches?
Divide by 2.54 to get total inches, then divide by 12. The whole number is the feet, and what's left over is the inches. For 165 cm, that's 64.96 in, which is 5 ft 4.96 in, or about 5 ft 5 in. The converter shows this line for any length of 12 inches or more.
What fraction of an inch is 1 cm?
1 cm is 0.3937 in, which is closest to 6/16, or 3/8 in (0.375 in). 5 mm is about 3/16 in, and 2 cm is about 13/16 in.
Why do some tape measures show both units?
Tapes with both scales save you the math. Because 2.54 isn't a round number, the two scales line up exactly only every 127 cm (50 in).
How this calculator is checked
Method: International yard and pound agreement (1959): 1 in = 25.4 mm = 2.54 cm exactly. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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