Convert CM to Inches

Centimetres to inches, the way you actually need it

Type a length in centimetres and get the answer three ways at once: as a decimal (66.929 in), as a fraction to the nearest sixteenth of an inch (66 15/16 in) – the way tape measures and rulers are marked – and in feet and inches (5 ft 6 15/16 in), the way heights are written in the US and UK. The converter also shows the formula with your number filled in, a table of the same length in every other unit (mm, m, km, ft, yd, mi), and a swap button for inches to centimetres.

One inch is defined as exactly 2.54 centimetres. That definition has been international since 1959, so the conversion is exact – there is no rounding in the factor, only in how many decimals you choose to display.

The formula

inches = centimetres ÷ 2.54, or equivalently inches = centimetres × 0.3937007874.

To go the other way: centimetres = inches × 2.54.

For feet and inches: divide the total inches by 12. The whole number is feet; the remainder is inches. Example: 170 cm ÷ 2.54 = 66.93 in; 66.93 ÷ 12 = 5 remainder 6.93 → 5 ft 6.93 in (about 5 ft 7 in).

Worked examples

• 30 cm ÷ 2.54 = 11.81 in – just under a foot (a standard school ruler).
• 15.6 inch laptop screen × 2.54 = 39.6 cm diagonal.
• A4 paper (21 × 29.7 cm) = 8.27 × 11.69 in.
• 160 cm height = 62.99 in = 5 ft 3 in.
• 180 cm height = 70.87 in = 5 ft 10 7/8 in.
• 55 cm cabin bag = 21.65 in (often quoted as 22 in).
• 2.5 cm = 0.98 in – roughly one inch, handy for quick estimates.

Mental-math shortcut

For a quick estimate, multiply centimetres by 4 and divide by 10: 50 cm × 4 = 200 → 20 in (exact: 19.69 in). This overestimates by about 1.6%. To go from inches to centimetres, multiply by 2.5 and add a little: 10 in × 2.5 = 25 → 25.4 cm. For heights, remember that 152.4 cm is exactly 5 ft, and each extra inch adds 2.54 cm.

Centimetres to inches chart

Inches to centimetres chart

Reading fractions of an inch

Imperial rulers and tape measures divide each inch into halves, quarters, eighths and sixteenths. The longest tick in the middle is 1/2; the next longest are 1/4 and 3/4; then the eighths (1/8, 3/8, 5/8, 7/8); and the shortest ticks are sixteenths. When the converter shows 66 15/16 in, look for the 66-inch mark and count fifteen of the smallest ticks beyond it – or, more simply, one tick before the 67-inch mark. A sixteenth of an inch is about 1.6 mm, which is the precision most woodworking, sewing and DIY projects need.

Where you meet cm and inches

A short history of the inch and the centimetre

The centimetre is one hundredth of a metre, the base unit of length in the International System of Units (SI). The metre was originally defined in 1793 as one ten-millionth of the distance from the North Pole to the equator, and since 1983 it has been defined by the distance light travels in a vacuum in 1/299,792,458 of a second. The inch has older roots: in many languages the word for inch also means thumb, and medieval English law defined it as the length of three barleycorns. Different countries' inches varied slightly until 1959, when the United States, United Kingdom, Canada, Australia, New Zealand and South Africa agreed on the international inch of exactly 25.4 millimetres. Today almost every country uses centimetres for everyday measurements, while the United States – and the UK for some uses such as heights and screen sizes – still commonly uses inches.

Accuracy and rounding

Because 1 in = 2.54 cm exactly, the only error comes from rounding the result. For most purposes, two decimal places of an inch (0.01 in ≈ 0.25 mm) are more than enough. Engineering drawings often use three decimals (thousandths of an inch, 'thou'). For woodworking and sewing, the nearest 1/16 in is standard; for heights, the nearest whole inch. The converter shows up to eight significant decimals so you can round to whatever your project requires.

Privacy

The converter runs entirely in your browser. Nothing you type is sent anywhere, there is no tracking of your values, and once the page has loaded it keeps working offline – handy on a building site, in a shop or on a plane.

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