Convert cm to in centimetres ↔ inches Free Online Secure
Type a value in centimetres and read it in inches at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert cm to in (centimetres ↔ inches)
| cm | in |
|---|---|
| 1 | 0.393700787402 |
| 2 | 0.787401574803 |
| 3 | 1.1811023622 |
| 5 | 1.96850393701 |
| 10 | 3.93700787402 |
| 20 | 7.87401574803 |
| 50 | 19.6850393701 |
| 100 | 39.3700787402 |
Where these units come from
The metre was first defined in 1793 as a ten-millionth of the distance from the equator to the North Pole — a definition nobody could check without surveying a quarter of the planet. It has been redefined four times since, each time to something steadier: a platinum bar, then a prototype kept in Paris, then a wavelength of krypton light, and since 1983 the distance light travels in vacuum in 1/299,792,458 of a second. The inch stopped being a separate thing in 1959, when six countries agreed to define it as exactly 25.4 mm. That agreement is why every conversion on this page between a metric and an imperial length is exact rather than measured: both sides now descend from the same definition.
Where you meet them
Millimetres are the working unit of engineering drawings and of anything made in a workshop; centimetres belong to tailoring, furniture and school rulers; metres to rooms, fabric and running tracks. Feet and inches survive in aviation altitudes worldwide, in American and British construction, and in the diagonal of every screen you have ever bought. Nautical miles are not a quaint survival — one is a minute of latitude, which is why ships and aircraft still navigate in them.
Questions people ask
Where is the centimetre used in everyday life?
For anything a person measures against their own body: height, clothing sizes, the length of a sleeve, the width of a shelf, the dimensions of a parcel. A centimetre is roughly the width of a fingernail, which makes it easy to picture. It is large enough to avoid long strings of digits and small enough that you rarely need a decimal.
Why is 1 inch exactly 25.4 mm?
Because in 1959 the standards bodies of the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed to make it so. Before that the American inch and the British inch differed in the seventh decimal place, which was enough to matter when parts made on one side of the Atlantic had to fit parts made on the other. The agreed value is a definition, not a measurement, so it will not be revised.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Waist sizes, screens and picture frames: when you need to convert cm to in
The centimetre is the everyday length of most of the world, and the inch is the everyday length of the places that shop in dollars. The two meet at the tape measure in a tailor's shop, on the box of a television, on the label of a pair of jeans ordered from an American website and on the page of a furniture catalogue that lists a sofa as 90 inches wide. This page is for the moment when the number you have is in centimetres and the number you need is in inches. Type a length and read it in inches at once; the answer comes from the exact definition of the inch, not from a rounded rule of thumb.
Because one inch is exactly 2.54 centimetres, the conversion is clean in one direction and awkward in the other. Dividing by 2.54 is easy for a machine and tedious for a person, which is why people look for a quick way to convert cm to in. Below you will find the factor, four worked examples, a short profile of each unit, a comparison, the situations in which people most often need the conversion, and the slips that spoil the result.
The arithmetic behind convert cm to in
One inch is exactly 2.54 centimetres
Since 1959 the inch has been defined as exactly 25.4 millimetres, so one centimetre is 1 ÷ 2.54 = 0.393701 inches, rounded. To convert cm to in, divide the number of centimetres by 2.54, or multiply it by 0.393701. Both give the same answer; the division uses the exact figure and the multiplication a rounded one, so for anything that matters use the division.
Four worked examples
A 30 cm ruler is 30 ÷ 2.54 = 11.81 inches, close to the familiar 12 of the imperial ruler. A 55 cm cabin bag is 21.65 inches, which is why airlines quote it as 22. A 180 cm person is 70.87 inches, or 5 feet 10.9 inches. A 100 cm length of ribbon is 39.37 inches, a little over a yard. Each is one division, and the box at the top of this page does it in an instant.
Doing it in your head
Multiply by four and divide by ten: 50 cm × 4 = 200, divided by 10 is 20 inches, against an exact 19.69. A closer estimate is to remember that 2.5 cm is about one inch and divide by 2.5, which you can do by doubling the centimetres and dividing by five: 50 × 2 = 100, divided by 5 is 20. Accuracy of one or two per cent is enough for most shopping.
Rounding
Clothes are sold in whole or half inches, so round to the nearest half. Screens use one decimal. Engineering drawings use three or four decimals.
The centimetre, the hundredth of a metre
A unit you can hold between finger and thumb
A centimetre is a hundredth of a metre, about the width of a fingernail or a pea. It is the unit of rulers, dress patterns, baby growth charts and the height of a child on a doorframe, and it gives numbers of a convenient size for things between a coin and a wardrobe. Because the metric system is decimal, a centimetre divides neatly into ten millimetres and ten of them make a decimetre, which is why measuring in centimetres rarely needs fractions.
Where it lives
Shoe sizes in some countries, height on a passport, the thickness of a mattress, the diagonal of a phone in some catalogues, and the length of a fish in a sports report are all stated in centimetres outside the United States. The symbol is cm, in lower case, with a space after the number.
The inch, a thumb's width
From thumbs and barleycorns
The inch comes from the Latin uncia, a twelfth, and in many languages the word for inch is also the word for thumb. Medieval English law defined it as the length of three barleycorns laid end to end. The American and British inches differed slightly until 1959, when the countries of the English-speaking world agreed on 25.4 millimetres exactly. That decision made the conversion factor a tidy decimal, 2.54, and it is why the page can show an exact result.
Where it lives
Inches measure television and monitor diagonals everywhere, tyre and wheel sizes, pipe diameters, nails and screws, the width of lumber, and clothing in the United States, Britain and Canada. A "32-inch waist" is common even in countries that otherwise think in centimetres. The symbol is in or a double prime mark, and you will see both on labels.
Centimetre and inch compared
The inch is 2.54 times longer than the centimetre, so a number of inches is smaller than the same length in centimetres: 100 cm is 39.37 in, but 100 in is 254 cm. That is why a "40-inch TV" sounds smaller than its metric twin, a 102 cm screen. A useful anchor is that your thumb is about 2.5 cm wide, one inch.
Choose the unit your reader is used to. Clothes, furniture and screens are better stated in both units; technical drawings follow the standard of their country. If you are unsure, give the metric figure first and the inch figure in brackets, or the other way round for an American audience.
Situations that call for convert cm to in
Clothes and tailoring
Waist, hip and inseam measurements are given in inches by most American and British brands and in centimetres by continental ones. A tailor in Milan may measure a chest of 102 cm, which is 40.2 inches, a size 40 in American jackets. A hem of 5 cm is about 2 inches, and a trouser inseam of 81 cm is 31.9 inches, which fits the common 32. Before ordering from an overseas shop, measure yourself in centimetres, convert cm to in and compare with the size chart; the chart in inches is nearly always the original.
Screens and furniture
A television diagonal of 139 cm is 54.7 inches, which the shop will call a 55. A laptop screen of 33.8 cm is 13.3 inches; 39.6 cm is 15.6 inches. When you compare, remember that screens are measured on the diagonal, not the width. For furniture, a 200 cm sofa is 78.7 inches, a standard 6 ft 6 in bed is 198 cm, and a 60 cm kitchen unit, the width of a standard dishwasher, is 23.6 inches. When you shop across borders, convert cm to in for each item before you check the space at home.
Photos, frames and prints
Photo sizes straddle the two systems. A 10 × 15 cm print is 3.9 × 5.9 inches, the familiar 4 × 6; 13 × 18 cm is 5 × 7; 20 × 30 cm is 7.9 × 11.8, close to 8 × 12; and 30 × 40 cm is 11.8 × 15.7, near 12 × 16. Frames are sold in inches in the United States, so a European print may need a mat. Always measure the print, not the label.
Hobbies, school and DIY
Knitting needles, sewing patterns and quilting blocks are often written in inches in English-language books and in centimetres in European ones. A quilt block of 30 cm is 11.8 inches. Pupils working with a ruler marked on both edges can check their sums: the 15 cm mark sits at 5.9 inches. DIY plans from American websites specify lumber in inches, and a 2 × 4 board is actually 1.5 × 3.5 inches, or 3.8 × 8.9 cm.
How the inch and the centimetre lined up
A century of nearly equal inches
For hundreds of years the inch meant different things in different places. The English inch, the Scottish inch and the French pouce differed by small amounts, and when machine parts began to be made in one country and assembled in another, the differences caused trouble. In 1959 the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed that the yard would be exactly 0.9144 metres, which made the inch exactly 25.4 millimetres. Anyone who wants to convert cm to in today is using that treaty without knowing it.
Why the inch will not go away
Inch-based standards are deeply embedded: pipe threads, screw sizes, tyre rims, paper sizes in North America, and the 19-inch rack in which servers are mounted worldwide. Changing them would mean changing tools and parts, and that is expensive. Even countries that went metric long ago, such as Germany and Japan, still use inches for monitor diagonals and tyre diameters. The inch survived because it is a convenient size, close to a thumb, and because it divides into halves, quarters and eighths without fuss.
The centimetre in the metric system
The metric system has no official place for the centimetre among the preferred prefixes of engineering, where millimetres and metres are favoured, yet the centimetre dominates everyday life. It is the unit of human size and household objects, and children learn it first. Sports, medicine, fashion and cartography all use centimetres where an engineer would use millimetres. A growth chart in a doctor's office, a hat size, a shoe length and the height of a high jump are almost always quoted in centimetres.
Keeping both scales in sight
Tapes with two edges
The best way to avoid arithmetic is a tape with centimetres on one edge and inches on the other. You read the length in the unit you need, and compare it with the other as a check. Sewing tapes are normally double-sided, with the inch side starting from the opposite end, so look for the printed zero before you measure. When you do need to convert cm to in for a written figure, the tape is a good test of your result.
Smartphone helpers
Phone apps measure with the camera and show both units, but their accuracy is limited to a centimetre or two. Use them for rough planning, such as checking whether a sofa will fit, and use a tape for anything that must be exact. A phone is no substitute for a ruler when the margin is a millimetre.
Precision, tolerances and tools
Rulers, tapes and callipers
A school ruler marked in centimetres and millimetres reads to half a millimetre, about 0.02 inches. A tailor's tape is accurate to a couple of millimetres, which is enough for clothes. A steel tape for carpentry reads to a millimetre or a sixteenth of an inch. Vernier callipers reach 0.02 mm, and micrometers 0.001 mm, or 0.00004 inches. The point is that the number of digits you keep after you convert cm to in should match the tool you used to measure, not the calculator you used to convert.
Tolerances and fit
In furniture and building, a tolerance of a few millimetres is normal. A fitted wardrobe measured at 244 cm is 96.06 inches, and no one will check the last two digits; but a door frame, a window or a kitchen worktop must be right to within a couple of millimetres, which is a twelfth of an inch. If a part is ordered from abroad, give both units and confirm which one the supplier will use.
Scaling drawings and maps
Architectural and map scales mix the two systems. A scale of 1:50 means 2 cm on the plan are 1 m in reality, and an American scale of 1/4 inch to the foot is 1:48. When convert cm to in on a scaled drawing, convert the real length first, then apply the scale, and the sums will not go wrong.
Measuring yourself before you order
Take the numbers in centimetres, then convert
When you buy clothes from a shop that uses inches, accurate body measurements matter more than any size label. Use a soft tape, stand relaxed and measure over thin clothing. For the chest, go around the fullest part under the arms; for the waist, around the narrowest point, usually above the navel; for the hips, around the widest part; for the inseam, from the crotch to the ankle bone. Write each number in centimetres, then convert cm to in and compare the results with the chart.
Between two sizes
If your waist is 83 cm, which is 32.7 inches, you sit between a 32 and a 34. Fit depends on the fabric: stretch denim tolerates the smaller size, stiff cotton asks for the larger. Read the reviews for notes on fit, and keep the return label. A good tape is cheap, and a shop's own measuring guide usually shows the exact points of the body to use.
More values for convert cm to in
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 cm = 0.0393701 in
- 0.5 cm = 0.19685 in
- 3 cm = 1.1811 in
- 4 cm = 1.5748 in
- 7 cm = 2.75591 in
- 15 cm = 5.90551 in
- 20 cm = 7.87402 in
- 75 cm = 29.5276 in
- 200 cm = 78.7402 in
- 500 cm = 196.85 in
- 2,000 cm = 787.402 in
- 10,000 cm = 3,937.01 in
Mistakes that happen when you convert cm to in
Multiplying by 2.54
The commonest slip is to multiply by 2.54 when you should divide. The inch is the bigger unit, so the number of inches is smaller than the number of centimetres. If your answer is larger than the figure you started with, check the direction.
Reading a diagonal as a width
A 55-inch television is 139.7 cm on the diagonal, not across. The width of a 16:9 set of that size is about 122 cm, and a cabinet must be wide enough for that. Measure the space for the width and the height, not for the diagonal.
Stopping at one digit
If a pair of trousers has a 81 cm inseam, 31.9 inches is a better answer than 32 for comparing with a chart that lists 31 and 33. Round only when the size chart requires it.
Quick answers about centimetres and inches
How many inches are in a centimetre?
0.393701 inches. To convert cm to in, divide by 2.54.
How many centimetres are in an inch?
Exactly 2.54 centimetres, by international agreement.
What is 100 cm in inches?
39.37 inches, a little over a yard.
What is 170 cm in feet and inches?
170 cm is 66.93 inches, or 5 feet 6.9 inches.
Is the conversion exact?
Yes, because the inch is defined exactly as 2.54 cm; only the displayed digits are rounded.
Is my number sent anywhere?
No. The calculation runs in your browser and nothing is uploaded.
Related pages and a last word
If you work with lengths regularly, these conversions are close by: Convert cm to mm, Convert cm to dm, Convert mm to in, Convert dm to in, Convert in to ft, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L. The reverse of this page is Convert in to cm, which uses the same definition backwards.
In short, to convert cm to in divide by 2.54, check that the answer is smaller than the starting figure and round to the precision of the tool you measured with. Your number stays on your device: the arithmetic is done locally, with no account and nothing to delete afterwards.