CM to Inches Converter (and Every Length Unit)

To convert cm to inches, divide the centimeters by 2.54, because one inch is exactly 2.54 cm. For example, 170 cm ÷ 2.54 = 66.93 inches, which is 5 feet 6.93 inches, or about 5 ft 6 15/16 in on a tape measure. To go back from inches to cm, multiply by 2.54: 12 in × 2.54 = 30.48 cm.

How to use the length converter

1. Type a number in the From box and pick its unit: millimeters, centimeters, meters, kilometers, inches, feet, feet + inches, yards, miles or nautical miles.
2. Pick the unit you want in the To box. The answer appears as you type. You can also type in the To box to convert the other way.
3. For heights and tape-measure readings, choose Feet + inches and type 5 ft 7 in, 5 7 or 5’7″. Inch fractions such as 3 5/8 work in any box.
4. Set the decimals and the inch fraction (1/16 is the usual tape-measure mark, 1/32 or 1/64 for fine work).
5. Open Show steps for the working, compare the two rulers, and use the table for other values of the same pair.

CM to inches formula

inches = centimeters ÷ 2.54

centimeters = inches × 2.54

The number 2.54 is not a rounded measurement. It is the definition of the inch: NIST Handbook 44 lists 1 inch = 2.54 centimeters (exactly). So dividing by 2.54 gives the exact answer, and any rounding happens only when you write the result down.

You will often see the shortcut “multiply by 0.3937”. It works because 1 ÷ 2.54 = 0.393700787…, but 0.3937 is rounded. For everyday lengths the difference is tiny (about 2 parts per million), yet dividing by 2.54 is both exact and easier to remember.

A quick mental check: 1 inch is a bit more than 2.5 cm, so 10 cm is a bit less than 4 inches (3.94 in), and 30 cm, a school ruler, is just under 12 inches (11.81 in).

Why one inch is exactly 2.54 cm

Since 1959 the inch, foot, yard and mile used in the United States have been defined from the meter. The yard is exactly 0.9144 m, so the foot (one third of a yard) is exactly 0.3048 m and the inch (one twelfth of a foot) is exactly 0.0254 m, or 2.54 cm. The mile is 5,280 feet, which makes it exactly 1.609344 km.

The international nautical mile, used at sea and in the air, is defined directly as 1,852 meters. It is about 1.15 statute miles. NIST’s Guide to the SI lists all of these factors as exact.

Because every unit is an exact multiple of the meter, the converter stores each one as a fraction of a meter and does the arithmetic with exact fractions. Rounding happens only at the very end, and the result is marked exact or rounded so you can see which one you got.

How to convert cm to feet and inches

Heights are usually written in feet and inches, so a single number of inches is only half the job.

1. Divide the centimeters by 2.54 to get inches.
2. Divide the inches by 12. The whole number is the feet.
3. The remainder (inches minus 12 × feet) is the inches left over.

Example: 183 cm. 183 ÷ 2.54 = 72.047 in. 72 ÷ 12 = 6 feet with 0.047 in left over, so 183 cm is 6 ft 0.05 in, practically 6 feet.

Going the other way: 5 ft 7 in. First turn everything into inches: 5 × 12 + 7 = 67 in. Then 67 × 2.54 = 170.18 cm.

Reading the answer on a tape measure

US tape measures mark inches in halves, quarters, eighths and sixteenths, not decimals. To turn a decimal inch into the nearest sixteenth, multiply the decimal part by 16 and round to a whole number.

Example: 30 cm. 30 ÷ 2.54 = 11.811 in. The decimal part is 0.811, and 0.811 × 16 = 12.98, which rounds to 13. So 30 cm is about 11 13/16 inches. The fraction is off by less than 1/32 inch, which is as close as you can read a 1/16 mark anyway.

If the number of sixteenths is even, simplify the fraction: 8/16 = 1/2, 12/16 = 3/4, 14/16 = 7/8. The converter does this for you and lets you choose 1/2 up to 1/64.

CM to inches chart

Length conversion factors

Common mistakes when converting length

• Multiplying when you should divide. Centimeters are smaller than inches, so the number of inches must be smaller. 10 cm is 3.94 in, not 25.4 in.
• Reading 5.7 feet as 5 ft 7 in. The decimal part is a fraction of a foot: 0.7 × 12 = 8.4, so 5.7 ft is 5 ft 8.4 in.
• Rounding too early. Use 2.54 exactly and round only the final answer, especially for long lengths.
• Mixing up the mile and the nautical mile. A nautical mile (1,852 m) is about 15% longer than a statute mile (1,609.344 m).
• Swapping the symbols. One mark (‘) means feet and two marks (“) mean inches, so 5’7” is 5 feet 7 inches.

Sources

Exact unit definitions were checked November 2026:

• NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement
• NIST Guide to the SI (SP 811), Appendix B.9: Factors for units listed by kind of quantity
• NIST Handbook 44, current edition

CM to inches practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How many inches is 1 cm?

One centimeter is 1 ÷ 2.54 = 0.3937 inches, a little less than 3/8 of an inch. It takes 2.54 centimeters to make one inch.

How tall is 170 cm in feet and inches?

170 cm ÷ 2.54 = 66.93 inches. Dividing by 12 gives 5 feet with 6.93 inches left over, so 170 cm is 5 ft 6.93 in, almost 5 feet 7 inches.

Is 1 inch exactly 2.54 cm?

Yes. Since 1959 the inch has been defined as exactly 2.54 centimeters, and NIST Handbook 44 lists it as exact. Only the reverse factor, 0.3937 inches per centimeter, is rounded.

How do I convert inches to cm?

Multiply the inches by 2.54. For example, 12 inches × 2.54 = 30.48 cm, and 6 inches × 2.54 = 15.24 cm.

What is the difference between a mile and a nautical mile?

A statute mile is 5,280 feet, exactly 1.609344 km. A nautical mile is exactly 1,852 meters, about 1.15078 statute miles. Nautical miles are used for sea and air navigation because one nautical mile is close to one minute of latitude.

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