Cm to inches converter

How to use it

1. Type a length. Write the number in the first field and choose its unit, for example 170 and centimeters. Comma or dot both work as the decimal mark.
2. Choose the target unit. Pick the unit of the second field. The result appears straight away, and you can type in the second field to convert the other way.
3. Read feet, inches and fractions. Under the result you see the length in feet and inches and rounded to the inch fraction you chose, ready for a tape measure. The ruler shows the same length on both scales.

The formula: 1 inch = 2.54 cm, exactly

Since 1 July 1959 the inch has been defined as exactly 25.4 millimeters. The United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed on this value in the international yard and pound agreement; before it, the American and British inch differed by a few parts per million. Because the definition is exact, the conversion is too: no rounding hides in the factor.

All the imperial units follow from the inch: a foot is 12 inches (30.48 cm), a yard is 3 feet (91.44 cm) and a mile is 1,760 yards. Internally the tool converts every value to micrometers using whole numbers, so going from inches to centimeters and back returns exactly the number you started with.

Feet and inches, and the fractions on a tape measure

Heights in the US and UK are written as feet plus inches. To convert 170 cm, divide by 2.54 to get 66.93 inches, then take out whole feet: 5 feet are 60 inches, leaving 6.93 inches. The other way works the same: 5 ft 9 in is 69 inches, or 175.26 cm.

Imperial tape measures are not marked in decimals but in halves, quarters, eighths and sixteenths of an inch. The tool rounds to the fraction you choose and reduces it, so 170 cm reads as 66 15/16 inches to the nearest sixteenth. A 19 mm pipe is close to 3/4 in, which is why it is often sold as a "3/4 inch" pipe.

Rounding to a fraction changes the value slightly. For woodworking 1/16 inch (about 1.6 mm) is usually enough; for machining, keep the decimal value.

Worked examples

Where you still meet inches

• Screens: TVs, monitors, laptops and phones are sold by their diagonal in inches all over the world.
• Clothes: jeans waist and leg length (W and L), and men's shirt collars in English-speaking countries.
• Tyres and wheels: the rim diameter is in inches (a 205/55 R16 tyre fits a 16-inch rim), even where the width is in millimeters.
• Plumbing and fittings: pipe threads such as 1/2 or 3/4 inch are nominal names and do not match the actual outer diameter.
• Photos and paper: 4 × 6 inch prints, US Letter and Legal sheets, and print resolution in dots per inch.

To size a floor or a wall after converting the measurements, use the square footage calculator. For body measurements, the BMI calculator accepts height in both centimeters and feet and inches.

Sources

• NIST, “SI Units – Length”: the international inch of exactly 25.4 mm and yard of exactly 0.9144 m, adopted from 1 July 1959 (Federal Register notice 59-5442). Checked 14/10/2026.
• NIST Special Publication 811 (2008), Appendix B.8, conversion factors for foot (0.3048 m) and mile (1,609.344 m). Checked 14/10/2026.
• NIST Handbook 44, Appendix C, general tables of units of measurement. Checked 14/10/2026.

The examples on this page are computed with the same code as the converter, so the numbers in the text always match the tool.

Frequently asked questions