Cm to Inches Converter

centimeters to inches — quick reference

The formula, worked line by line

The inch is defined by the centimeter, not measured against it. The International Yard and Pound Agreement signed on 1 July 1959 by the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa fixed the yard at exactly 0.9144 meters.

Divide that by 36 and the inch falls out as exactly 0.0254 meters, or 25.4 millimeters, and the foot as exactly 0.3048 meters. Before 1959 the American and British inches differed in the seventh decimal place because each was tied to its own physical yard bar.

So centimeters to inches is a division by an exact constant, and the only approximation anywhere in the process is however many decimal places you choose to show. Reading a height takes one more step, because feet and inches is a mixed-radix notation: twelve inches to the foot, with the remainder staying in inches rather than becoming a decimal fraction of a foot.

inches = centimeters ÷ 2.54
       = centimeters × 0.393700787…
feet = whole part of (inches ÷ 12), remainder stays in inches
170 cm → 170 ÷ 2.54 = 66.929134 in → 5 ft 6.93 in

The US survey foot wrinkle

One historical wrinkle that still turns up in US land records. From 1959 until the end of 2022 the United States maintained two feet: the international foot of exactly 0.3048 meters, and the US survey foot of 1200/3937 meters, or about 0.30480061 meters, retained for geodetic and land surveying. The difference is roughly two parts per million, about an eighth of an inch per mile, which is invisible on a room measurement and substantial across a state plane coordinate grid.

NIST and the National Geodetic Survey deprecated the US survey foot on 31 December 2022, so from 1 January 2023 there is one foot in US practice. If you are reading a plat, a legal description or a coordinate value dated before 2023, check which foot it used before converting.

How to use the cm to inches converter

Centimeters reach US readers more often than you would expect. A height printed on a passport or listed on a dating profile, a television or monitor whose spec sheet is metric, the dimensions on an imported product page, a doctor abroad reading a wall-mounted stadiometer, the sizing chart on a European clothing site: all of them hand over a metric number and leave the interpretation to you.

This converter turns centimeters into inches you can picture, and Swap runs it the other way when you are the one entering inches. The tool divides by 2.54 exactly, because that is the international definition of the inch rather than an approximation of it, so the answer is not a best guess but the actual value with the display rounded to two places.

Height is the classic case and also the one where people go wrong, because it takes two steps rather than one. 170 cm is 66.93 inches, and 66.93 inches is 5 feet 6.93 inches, which rounds to 5 feet 7.

The mistake is trying to jump straight from centimeters to feet and reading the decimal part of the feet as inches: 170 cm is 5.577 feet, and 0.577 is not 7 inches, it is 6.93. Always convert to inches first, then divide by 12 and keep the remainder in inches.

For a mental estimate, divide the centimeters by 2.5. It is close to the true 2.54 and easy to do in your head, but it reads about 1.6 percent high, so 170 cm comes out as 68 inches against a true 66.93, an error of just over an inch.

A second shortcut is more accurate and almost as fast: take four tenths of the centimeters and then subtract one and a half percent, since 0.4 is the reciprocal of 2.5.

In practice, use the rough version to judge whether a number is in the right ballpark, and use the exact factor whenever the answer drives a physical fit, a cut, a mount or anything that goes on a record. Being an inch out on a shelf bracket costs a trip back to the hardware store.

Screen sizes: the diagonal in both units

Screens and displays are quoted by their diagonal, and manufacturers outside the US often print that diagonal in centimeters while the marketing name stays in inches. Because the marketing name is a whole number of inches, the metric figure is always a multiple of 2.54: a panel described as 139.7 cm is the 55-inch class, 165.1 cm is 65 inches, and 190.5 cm is 75 inches.

On a desk, 68.58 cm is a 27-inch monitor and 60.96 cm is a 24-inch one. If a spec sheet gives a diagonal that is not a clean multiple of 2.54, it has been rounded, and the panel is whichever inch class it sits nearest. Converting first tells you which price bracket you are actually comparing.

Every centimeters value, worked out

136 common centimeters figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask