CM to Inches Converter

Why there are exactly 2.54 centimetres in an inch

The inch is defined from the metre: since 1959, 1 inch = 2.54 cm exactly. Nothing is rounded in that figure, so converting centimetres to inches is always a single exact division. One centimetre is 1/2.54 inch, or about 0.3937 inches — a little under four tenths of an inch.

That definition was agreed between the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa to end small differences between their national inches, and it is the basis of every ruler, tape measure and conversion factor in use today.

How to convert cm to inches

Divide the centimetres by 2.54. If multiplication is easier, multiply by 0.3937 instead — both give the same answer to four significant figures, which is more than any tape measure can show. For lengths over a foot, it is usually clearer to split the answer into feet and inches — divide the inches by 12, keep the whole number of feet, and the remainder is the inches.

For a slower walk-through with practice questions, see how to convert cm to inches. To convert the other way, multiply inches by 2.54 or use the inches to cm converter.

Height: cm to feet and inches

Height is the most common reason people convert centimetres. Most of the world measures height in cm, while the US and UK usually say feet and inches:

For any height, the height converter gives feet and inches directly, and the cm to feet converter gives decimal feet.

Clothing and body measurements

Clothing size charts from European and Asian brands give waist, chest, hip and inseam measurements in centimetres, while American charts use inches. Measure yourself with a soft tape, then convert — or compare the chart with these typical values:

Jeans sold with a “W32” waist mean 32 inches, about 81 cm. For shoes, rings, hats and gloves use the dedicated shoe size, ring size and clothing size converters, which handle the sizing systems as well as the units.

Everyday sizes in cm and inches

Product listings, airline rules and paper sizes are often given in centimetres. These conversions come up again and again:

TV and monitor sizes are a special case: they are sold by the diagonal in inches almost everywhere. A 55-inch TV is 139.7 cm across the diagonal; the TV size calculator works out its width and height.

Centimetres to inch fractions

A tape measure marked in inches shows fractions, not decimals. This table gives the nearest 1/8 and 1/16 inch for small centimetre values:

For any value and finer precision (1/32 or 1/64 inch), use the cm to inches fraction calculator, which also shows the rounding error.

Quick mental estimate: multiply by 0.4

Multiplying by 0.4 — or dividing by 2.5 — is easy to do in your head and lands within about 1.6% of the exact answer. It always comes out slightly high:

Useful anchors: 2.5 cm is about an inch, 30 cm is about a foot (11.8″), and 1 metre is about 39.4 inches — a little more than a yard.

Reading centimetres and inches on a ruler

On a dual ruler the metric edge has numbered centimetre marks with ten millimetre lines between each; the imperial edge has numbered inches divided into halves, quarters, eighths and sixteenths. Every 2.54 cm on the metric edge lines up with one inch on the other, so 5.08 cm meets the 2″ mark and 30.48 cm meets 12″. A standard 30 cm ruler is therefore slightly shorter than a 12-inch ruler. To measure small objects without a ruler, the online ruler works on screen after calibration.

Square and cubic centimetres

The 2.54 factor applies to lengths only. For areas, the factor is squared: 1 square inch = 2.54 × 2.54 = 6.4516 cm², so divide square centimetres by 6.4516 to get square inches. For volumes it is cubed: 1 cubic inch = 16.387 cm³ (16.387 ml). A 20 × 30 cm baking tray is 600 cm², which is 93 square inches — not 600 ÷ 2.54. Convert each side first (7.87″ × 11.81″) and multiply, or divide the area by 6.4516; both give the same answer.

Who uses centimetres and who uses inches?

Almost every country uses centimetres for everyday lengths — clothing, furniture, body measurements and school work. The United States uses inches for most of these, and the United Kingdom mixes both: people often give their height in feet and inches and screen sizes in inches, while shops, schools and official measurements use centimetres. Canada is similar, with many products labelled in both. Scientific and medical work everywhere uses metric units. If you buy from overseas, compare sizes in one unit — converting with this tool avoids surprises such as a “60 cm” cabinet that is 1 cm narrower than a 24-inch space.

Common mistakes

• Multiplying instead of dividing. Inches are larger than centimetres, so the number of inches must be smaller.
• Using 2.5 for exact work. It is fine for estimating but makes a 1.6% error — 4 mm on a 25 cm measurement.
• Writing 5.6 feet for 5 ft 6 in. 5.6 ft is 5 ft 7.2 in. Keep feet-and-inches and decimal feet separate.
• Confusing cm and mm. Divide millimetres by 25.4, not 2.54 — or use the mm to inches converter.