Centimeters to Inches Converter

How to convert centimeters to inches (the formula)

To convert centimeters to inches, divide by 2.54: inches = centimeters ÷ 2.54. Equivalently, multiply by 0.39370079. Because one inch is exactly 2.54 cm, dividing by that number gives the precise answer with no approximation in the factor itself.

Two examples make the direction obvious. A standard sheet of A4 paper is 21 cm wide, and 21 ÷ 2.54 = 8.27 inches. A 180 cm person is 180 ÷ 2.54 = 70.87 inches tall. In both cases the number of inches is smaller than the number of centimeters, because an inch is the bigger unit, a useful check that you divided rather than multiplied.

This page converts both ways as you type. Enter a value in the centimeters box and the inches box fills in; enter inches and the centimeters update instead. That makes it easy to go back and forth while you compare a metric spec to an imperial tape measure.

Why the conversion factor is 0.393701

The factor 0.393701 is one divided by 2.54. Since 1959 the international inch has been defined as exactly 2.54 centimeters under the yard-and-pound agreement signed by the US, UK, Canada, Australia, New Zealand and South Africa. Inverting that exact definition gives 1 cm = 0.3937007874… inches, a repeating decimal that never terminates.

That is why you see the factor written to different lengths, 0.39, 0.3937, 0.393701, depending on how much precision a source needs. The underlying value never changes; only the number of digits shown does. For everyday work, three or four decimal places is more than enough. For engineering or scientific work, keep every digit your software provides and round only at the end.

The exact centimeter-to-inch relationship is documented in NIST SP 811, the US federal guide to SI usage, and in the international SI Brochure published by the BIPM. Both confirm 1 in = 2.54 cm exactly, so 1 cm = 1/2.54 in exactly.

Centimeters to inches conversion chart

This chart covers both directions for the values people search for most. The centimeter-to-inch column is rounded to four decimal places.

Anchor to remember: 2.54 cm is one inch, so 5 cm is just under two inches and 30 cm is just under twelve inches (one foot).

Worked examples: common cm to inches conversions

Four conversions US users ask for constantly, each worked with the exact factor.

• A 180 cm height: 180 ÷ 2.54 = 70.87 inches, or 5 ft 10.9 in. Split the decimal to get feet: 70.87 ÷ 12 = 5 remainder 10.87.
• A 30 cm ruler: 30 ÷ 2.54 = 11.81 inches, which is why metric rulers are a touch shorter than 12-inch rulers.
• A 60 cm width shelf: 60 ÷ 2.54 = 23.62 inches, handy when fitting metric shelving into an imperial cabinet.
• A 100 cm length: 100 ÷ 2.54 = 39.37 inches, which is one meter and just over a yard.

To turn a decimal-inch result into feet and inches, divide the total inches by 12 to get feet, then multiply the fractional part back by 12 to get the leftover inches. That two-step move is the fastest way to read a height off a metric chart.

Centimeters to inches for height and clothing sizes

Two areas where cm-to-inches matters most for US users are height and clothing.

Height. Most of the world states height in centimeters, so a person described as "180 cm" needs converting before most Americans can picture it. Divide by 2.54 to get 70.87 inches, then split into feet and inches for 5 ft 10.9 in. A common shortcut is to remember that 152 cm is almost exactly 5 ft, and each additional 2.54 cm adds one inch.

Clothing and body measurements. European and Asian clothing is sized in centimeters for the waist, chest and inseam. A 76 cm waist is 76 ÷ 2.54 = 29.9 inches, so it is a US 30. A 96 cm chest is 37.8 inches. Getting these right prevents returns, because a two-centimeter error is almost a full inch, enough to change the fit.

The same math applies to furniture, bicycles and screen sizes. Whenever a spec is metric and your tape is imperial, divide the centimeters by 2.54.

Common cm-to-inches mistakes to avoid

The arithmetic is simple, but a few habits cause most wrong answers.

• Multiplying when you should divide. cm is the smaller unit, so the inches value must come out smaller. If your inches number is bigger than your cm number, you multiplied by 2.54 instead of dividing.
• Using 2.5 instead of 2.54 and calling it exact. The shortcut is fine for a rough idea, but 2.5 introduces about a 1.6% error, which is nearly 3 cm over a two-meter length.
• Forgetting to split feet and inches. A result of 70.87 inches is not "5 foot 70", divide by 12 to get 5 ft 10.9 in.
• Rounding mid-way. Keep full precision until the final step, then round the answer.

If a conversion looks off, sanity-check it: one inch is 2.54 cm, so there should be roughly 2.5 centimeters for every inch. Multiply your inches answer by 2.54 and you should land back on the centimeter value you started with.

Centimeters to inches: quick mental math

You will not always have the calculator open, so it helps to carry a few reference points and a rough rule in your head.

The rule: divide the centimeters by 2.5, then knock off about 1.6%. For 100 cm that gives 100 ÷ 2.5 = 40, and the exact value is 39.37 inches, so the estimate is a touch high. For 50 cm it gives 20 versus the exact 19.69 inches. The estimate is good to within an inch over typical distances.

• 2.54 cm = 1 inch (exact)
• 5 cm ≈ 2 inches
• 10 cm ≈ 4 inches
• 25 cm ≈ 10 inches
• 30 cm ≈ 12 inches (one foot)
• 100 cm ≈ 39.4 inches (one meter)

Another approach is to work in feet. Since 30.48 cm is one foot, divide centimeters by 30.48 to get feet directly: 180 cm ÷ 30.48 = 5.91 feet, or about 5 ft 11 in. For quick comparisons, is this shelf closer to 5 or 6 feet?, the feet route is faster than the inches route because the numbers stay small. Use the exact calculator above whenever a measurement will be cut, drilled or ordered.

Sources: NIST Letter Circular 1033 (the 1959 yard-and-pound agreement).

Where these conversion factors come from

The relationship between centimeters and inches is fixed by international agreement rather than by local convention. The values used on this page follow the NIST guide to the SI (US Department of Commerce) and the BIPM SI Brochure, the two documents that define the exact values used worldwide.

Because these factors are exact by definition rather than measured, converting a number and converting it back always returns the number you started with, there is no rounding drift to worry about.