Convert cm² to in² square centimetres ↔ square inches Free Online Secure
Type a value in square centimetres and read it in square 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 cm² to in² (square centimetres ↔ square inches)
| cm² | in² |
|---|---|
| 1 | 0.155000310001 |
| 2 | 0.310000620001 |
| 3 | 0.465000930002 |
| 5 | 0.775001550003 |
| 10 | 1.55000310001 |
| 20 | 3.10000620001 |
| 50 | 7.75001550003 |
| 100 | 15.5000310001 |
Where these units come from
Square units need no definition of their own: a square metre is a metre by a metre, and everything follows from the length. The land measures are older and stranger. The acre began as the land a yoke of oxen could plough in a day, which is why it was long and thin rather than square — one chain by one furlong, 4840 square yards. The hectare and the are came out of the French Revolution, when land had to be measured in something decimal; neither belongs to the International System, but both were kept for land because a hectare is a comfortable size to picture and a square metre is not. Since the 1959 agreement on the yard, the acre is exactly 4046.8564224 square metres, so the conversions on this page are exact rather than approximate.
Where you meet them
Square metres price flats, size carpets and decide how much paint a wall needs; square feet do the same work in the United States and in much of the property market worldwide. Hectares belong to farmland, forests and planning permissions; acres to land deeds in the English-speaking world. Square kilometres and square miles are for countries, lakes and fires. Square centimetres and square millimetres live in workshops, on datasheets and anywhere a cross-section matters.
Questions people ask
Why does a square metre hold 10,000 square centimetres?
A metre is 100 centimetres, and area multiplies length by length, so a square metre is 100 × 100 = 10,000 square centimetres. It is a common slip to use 100, which is the factor for length. Whenever you convert an area, square the factor you would use for the length.
How many square millimetres is a square inch?
Exactly 645.16, or 6.4516 square centimetres. The figure follows from the inch being exactly 25.4 millimetres: squaring 25.4 gives 645.16. Square inches turn up in the pressure unit psi, in the sizes of screens and prints, and in small component specifications.
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.
Small areas, two systems: from square centimetres to square inches
Square centimetres are the metric unit for things you can hold in your hand: a stamp, a credit card, the screen of a phone, a photo print. Square inches are what American and British manuals use for exactly the same things, and they appear on tyre pressure labels, cutting boards, baking tins and pizza menus. To convert cm² to in² you multiply by 0.155, so 100 cm² is 15.5 in², and 645 cm² is 100 in². The number looks small, but it is easy to mistake for the linear factor between centimetres and inches, which is quite different. This page multiplies as you type, and the text below shows where these small areas matter.
You will find the rule with worked examples, short profiles of both units, a comparison, a long tour of real situations and a list of the mistakes people make most often. The calculation runs in your browser and nothing you type is sent anywhere.
How to convert cm² to in²: multiply by 0.155
The rule
One square centimetre is 0.15500031 square inches. To convert cm² to in², multiply the square centimetres by 0.155. So 10 cm² is 1.55 in², 50 cm² is 7.75 in², 200 cm² is 31 in² and 1,000 cm² is 155 in². For the reverse, one square inch is 6.4516 cm², so multiply inches by 6.4516 or divide by 0.155.
Worked examples
A postage stamp of 4 cm² is 0.62 in². A credit card of 46 cm² is 7.13 in². A sheet of A5 paper of 311 cm² is 48.2 in². A baking tray of 755 cm² is 117 in². For a mental estimate, divide by 6.5: 650 cm² gives 100 in², and the exact value is 100.75.
Why the factor is not 0.394
One centimetre is 0.3937 inch, but an area is a length times a length, so the factor is squared: 0.3937 times 0.3937 is 0.155. Using the linear factor on an area is the most frequent mistake, and it overstates the answer by two and a half times.
A quick check
A square inch is much bigger than a square centimetre, so the number of square inches is much smaller. If your “convert cm² to in²” calculation gave you a bigger number than you started with, you divided instead of multiplying.
The square centimetre
A square one centimetre wide
The square centimetre is one hundredth of a metre on each side, which makes it 100 square millimetres or 0.0001 square metres. It is used wherever sizes are small: packaging, labels, biology, jewellery, electronics and school geometry. A fingernail is about 1 to 1.5 cm², a coin about 4 to 6 cm².
Where you meet it
Product specifications, medical dressings, solar cell data sheets and printing plates all use square centimetres. For anything bigger than a few hundred, square decimetres or square metres take over.
The square inch
An inch by an inch
The square inch is the area of a square 2.54 cm on a side, which is 6.4516 cm². It is used in the United States and the United Kingdom for small surfaces, and it is the basis of pressure in pounds per square inch, psi. A postage stamp is about 0.6 in², a credit card 7.1 in², a pizza 12 inches across 113 in².
Where it is used
Tyre labels, engine specifications, hobby cutting mats, picture frames and screen sizes all lean on inches and square inches, even in countries that are otherwise metric.
Square centimetre and square inch compared
A square inch is about 6.5 square centimetres, so the metric unit is the finer one. A card measured in cm² will have a figure about 6.5 times larger than the same card in in². Both units describe small areas, but they feel different: 20 cm² is a small sticker, 3.1 in² is the same sticker.
The unit you use depends on your audience. An American manual that says 12 in² may mean nothing to a European reader, who would prefer 77 cm². The conversion is pure multiplication, and the only risk is using the wrong factor.
Where the conversion appears
Pizza and kitchen
A 12 inch pizza has an area of 113 in², which is 730 cm². A 16 inch pizza has 201 in², 1,297 cm². A baking tin of 9 by 13 inches has 117 in², 755 cm². Recipes from the United States need a “convert cm² to in²” calculation before you pick the pan.
Electronics and screens
A smartphone screen of 6.1 inches diagonally has an area of about 90 cm², 14 in². A tablet of 11 inches has about 330 cm², 51 in². Reviews compare panels by the area they give you, and the metric number can look larger.
Medicine and the body
The palm of an adult hand, with the fingers, is about 1 per cent of the body surface, roughly 170 cm², 26 in². Doctors use the palm to estimate the extent of burns, and dressings are sold in cm² or in², so the conversion helps match them.
Credit cards and stamps
A credit card is 85.6 by 54 mm, so 46.2 cm², or 7.16 in². A standard postage stamp of 25 by 30 mm has 7.5 cm², 1.16 in². Cards, stamps, tickets and passes follow strict international standards, and the dimensions in both unit systems appear on manufacturers' sheets.
Mouse pads and desk mats
A desk mat of 90 by 40 cm covers 3,600 cm², 558 in². An American one of 36 by 16 inches, 576 in², is almost identical. A gaming mouse pad of 25 by 21 cm, 525 cm², is 81 in². Online shops list the dimensions in both units, but not always accurately.
Floor tiles
A tile of 30 by 30 cm has 900 cm², 139.5 in². A 12 inch tile is 144 in², 929 cm². Tiles sold abroad look the same, but the grout lines and the layout change by a few millimetres. A “convert cm² to in²” calculation before you order avoids mismatched rows.
Cakes, pies and pans
A round tin of 24 cm diameter has an area of 452 cm², 70 in². A 9 inch pie dish has 63.6 in², 410 cm². Recipes written for one will fit the other with only small changes, as the areas are within 10 per cent. This is useful when your pan does not match the recipe.
Rounding
The factor 0.155 is a good approximation, since the exact value is 0.15500031. For craft and cooking, one decimal is enough. For electronics and engineering, use at least three significant figures. Do not round before you multiply.
Spreadsheet use
Put square centimetres in column A and write =A2*0.15500031 in column B. For the reverse, use =A2*6.4516. Add a column showing the ratio to check that the results are consistent. Format with one or two decimals.
Teaching the idea
On graph paper with centimetre squares, draw a square of 2.54 cm on a side. Count the squares inside: about 6.45. That is a square inch in cm², and the class can see that the square factor is not the linear factor. The picture sticks better than the formula.
Labels and stickers
A label of 5 by 3 cm is 15 cm², 2.3 in². A shipping label of 4 by 6 inches is 24 in², 155 cm². Printers set the layout in whichever unit the template uses, so a mix of the two causes cropped designs. Convert before you send artwork.
Glass, mirrors and picture frames
A picture frame of 20 by 25 cm has a glass area of 500 cm², 77.5 in². An 8 by 10 inch frame has 80 in², 516 cm². The standard frame sizes in the two systems nearly coincide, but the opening is always slightly smaller than the outside size.
Fingerprints, coins and small parts
A one euro coin has a face of about 4.2 cm², 0.65 in², and a US quarter 4.6 cm², 0.71 in². A fingerprint covers roughly 2 to 3 cm², 0.3 to 0.5 in². Collectors and forensic experts record such small areas in whichever unit their country uses, and a “convert cm² to in²” calculation helps when an article from the other side of the ocean quotes the surface of an object.
Skin, dressings and medical patches
A standard plaster of 7.5 by 2.5 cm has 18.75 cm², 2.9 in². A large wound dressing of 10 by 10 cm covers 100 cm², 15.5 in². Medicated patches are labelled by their area, because the dose released depends on how much skin they touch. A nurse reading a leaflet in inches can convert the figure and compare it with the metric packs on the shelf.
Paper sizes
An A4 sheet is 21 by 29.7 cm, 623.7 cm², 96.7 in². A US Letter sheet is 8.5 by 11 inches, 93.5 in², 603 cm². They are almost the same area, which is why printers handle both. An A5 sheet is exactly half an A4, 311.85 cm², 48.3 in². When you convert cm² to in² for paper, check the standard first.
Printed circuit boards
A small circuit board of 5 by 5 cm has an area of 25 cm², 3.9 in². A microcontroller board such as the classic Arduino Uno measures 68.6 by 53.4 mm, 36.6 cm², 5.7 in². Board houses quote prices per square inch in the United States and per square centimetre elsewhere, so the conversion shows which quotation is cheaper.
Windows, screens and glass panels
A laptop screen of 15.6 inches diagonal covers about 1,000 cm², 155 in². A small window pane of 30 by 40 cm is 1,200 cm², 186 in². Glaziers quote glass in square feet in some countries and in square metres in others, but small panes are still cut and priced in square centimetres or inches, so a quick conversion is useful.
Biology and microscope slides
A microscope slide of 76 by 26 mm has 19.8 cm², 3.1 in². A cover slip of 22 by 22 mm has 4.84 cm², 0.75 in². Scientists report counts per square centimetre, such as cells per cm², while manuals for American equipment use square inches for the stage area. Matching units is necessary for correct density estimates.
A scale for the imagination
To feel the difference, picture a sticky note of 7.6 by 7.6 cm: 57.8 cm², almost exactly 9 in². A playing card has 55.9 cm², 8.7 in². A smartphone has about 100 cm², 15.5 in², roughly the area of two playing cards laid side by side. These everyday objects give a quick way to judge whether a number in either unit is reasonable, and a “convert cm² to in²” calculation done afterwards confirms it. If the result seems far from your mental picture, check the exponent on the unit: a missing square is the usual cause.
Photo prints
A 10 by 15 cm print has 150 cm², 23.3 in². A 4 by 6 inch print has 24 in², 154.8 cm². The two sizes are nearly identical, but the paper stock, the frame and the album pocket are cut for one or the other. Check the area when you buy a frame abroad.
Solar cells
A standard monocrystalline solar cell of 156 by 156 mm covers 243 cm², 37.7 in². A panel with 60 cells uses about 1.46 m² of cell area, 2,260 in². Datasheets from different countries mix cm², in² and m², so the data can look inconsistent unless you convert.
Tyre contact patch and psi
A car tyre touches the road with an area of about 150 cm², 23 in², per wheel, so the four together carry the car on about 600 cm². At 2.2 bar, 32 psi, this contact patch holds up around 330 kg. Pressure in psi is force per square inch, so understanding both area units lets you reason about grip and load.
Pressure under a shoe
A stiletto heel of 1 cm² under a 60 kg person produces about 6 kg per cm², which is 85 psi, more than a car tyre. A flat shoe of 200 cm² produces 0.3 kg per cm², 4.3 psi. The same weight, spread over different areas, gives very different pressure.
Cutting mats and craft
A cutting mat of 12 by 18 inches is 216 in², 1,394 cm². A smaller one of 30 by 45 cm is 1,350 cm², 209 in². Craft suppliers list sizes in both systems, and designers who share patterns need to convert templates so they fit the mat.
Petri dishes and laboratory plates
A standard petri dish of 100 mm diameter has a surface of 78.5 cm², 12.2 in². A six well plate has wells of about 9.6 cm², 1.5 in², each. Laboratory specifications use cm² because cell density is stated per cm², so a “convert cm² to in²” calculation lets a lab compare protocols published in different units.
Sandpaper and abrasive sheets
A sheet of sandpaper of 9 by 11 inches is 99 in², 639 cm². Sanding blocks, discs and belts are listed by size, and users compare the price per unit area. A disc of 125 mm diameter has 123 cm², 19 in².
More values for convert cm² to in²
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 cm² = 0.0155 in²
- 0.5 cm² = 0.0775002 in²
- 3 cm² = 0.465001 in²
- 4 cm² = 0.620001 in²
- 7 cm² = 1.085 in²
- 15 cm² = 2.325 in²
- 20 cm² = 3.10001 in²
- 75 cm² = 11.625 in²
- 200 cm² = 31.0001 in²
- 500 cm² = 77.5002 in²
- 2,000 cm² = 310.001 in²
- 10,000 cm² = 1,550 in²
Mistakes when you convert cm² to in²
Using the linear factor
The factor between cm and in is 0.394, between cm² and in² it is 0.155. If you used 0.394, your answer is 2.5 times too big.
Dividing by 2.54
For area, divide by 6.4516, not by 2.54.
Forgetting the square symbol
cm and cm² are different units. Check that each number you copy carries the exponent.
Quick answers
How many square inches in a square centimetre?
0.155.
How do I convert cm² to in²?
Multiply by 0.155.
How many square centimetres in a square inch?
6.4516.
What is 100 cm² in square inches?
15.5 in².
Does my number leave my device?
No. The calculation runs in your browser.
Related pages and a last word
If you work with small areas, these conversions are close at hand: Convert cm² to mm², Convert cm² to m², Convert mm² to in², Convert ft² to in², Convert in² to ft², Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. The reverse of this page is Convert in² to cm².
In short, to convert cm² to in² multiply by 0.155, remember that the area factor is the square of the length factor, and keep the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.