Convert in² to cm² square inches ↔ square centimetres Free Online Secure
Type a value in square inches and read it in square centimetres 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 in² to cm² (square inches ↔ square centimetres)
| in² | cm² |
|---|---|
| 1 | 6.4516 |
| 2 | 12.9032 |
| 3 | 19.3548 |
| 5 | 32.258 |
| 10 | 64.516 |
| 20 | 129.032 |
| 50 | 322.58 |
| 100 | 645.16 |
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
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.
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.
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.
American small areas in metric: from square inches to square centimetres
Engine manuals, hydraulic catalogues, hardware packaging and kitchen equipment from North America describe small areas in square inches. If you work in metric, you need to turn them into square centimetres before you can compare them with a European datasheet. To convert in² to cm² you multiply by 6.4516, which is the square of the 2.54 centimetres in an inch. So 10 in² is 64.5 cm² and 100 in² is 645.2 cm². This page multiplies as you type, and the text below shows where the conversion matters in engines, hydraulics, cooking and hobbies.
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 most frequent mistakes. The calculation runs in your browser and nothing you type is sent anywhere.
How to convert in² to cm²: multiply by 6.4516
The rule
One square inch equals exactly 6.4516 square centimetres. To convert in² to cm², multiply the number of square inches by 6.4516. So 2 in² is 12.9 cm², 5 in² is 32.3 cm², 20 in² is 129 cm² and 50 in² is 322.6 cm². To go back, divide square centimetres by 6.4516, or multiply by 0.155.
Worked examples
A piston with a bore of 3.5 inches has an area of 9.62 in², which is 62.1 cm². A hydraulic cylinder of 4 inches bore has 12.57 in², 81.1 cm². A skillet of 10 inches diameter has a cooking surface of 78.5 in², 506.7 cm². For a rough estimate, multiply by 6.5 and subtract a little: 10 in² gives 65, against 64.5 exactly.
The square of 2.54
An inch is 2.54 centimetres, so a square inch is a square of 2.54 by 2.54 centimetres, whose area is 6.4516 cm². This is why the factor for areas is not 2.54. Using 2.54 on an area makes the answer two and a half times too small, a common slip.
A quick check
The square centimetre is smaller than the square inch, so the number must get bigger, about six and a half times. If your “convert in² to cm²” calculation gave you a number only two and a half times bigger, you used the linear factor.
The square inch
One inch by one inch
The square inch is the area of a square one inch on a side, which equals 6.4516 cm², 0.00064516 m² or 1/144 of a square foot. It is the base of pressure in pounds per square inch, psi. In the United States it is used for engines, tools, small parts, paper and cookware.
Where it appears
Hardware packaging, engine bore sizes, brake and clutch data, hydraulic cylinders, and kitchen equipment such as pans and pizza stones.
The square centimetre
A hundredth of a metre on a side
The square centimetre is the area of a square 1 cm by 1 cm, 0.155 square inches. It is the metric unit for small surfaces: packaging, labels, textiles, medical dressings and biology. Pressure on small areas is often stated in newtons or kilograms per square centimetre.
Where it appears
European datasheets for gaskets, pistons and cylinders, as well as school geometry and craft guides, use square centimetres.
Square inch and square centimetre compared
A square inch is about six and a half times as big as a square centimetre. A small object that has 4 in² has 25.8 cm². The two units belong to the same scale, but their numbers differ, and engineers who read a drawing from the other system must convert carefully to avoid fits that are too tight or too loose.
The difference matters most when the area is multiplied by a pressure. A pressure of 100 psi on 12 in² produces 1,200 pounds of force; in metric, 6.9 bar acting on 77.4 cm² produces 534 kilograms force, the same force in other units.
Where the conversion appears
Engines and pistons
The bore of an American engine is given in inches. A bore of 4.0 inches has a piston area of 12.57 in², 81.1 cm². An eight cylinder engine with that bore has a total piston area of 100.5 in², 649 cm². Specialists compare engines across systems with a “convert in² to cm²” calculation on the area.
Hydraulic cylinders
A cylinder with a 3 inch bore has an area of 7.07 in², 45.6 cm². At a pressure of 2,000 psi, 138 bar, it pushes with 14,140 pounds, 6,400 kg. Catalogues from American makers give the bore in inches and the pressure in psi, while European ones use millimetres and bar.
Cookware
A cast iron skillet of 12 inches has a surface of 113 in², 730 cm². A 14 inch pizza stone has 154 in², 993 cm². A half sheet pan of 18 by 13 inches has 234 in², 1,510 cm². Recipes from American sources use these dimensions, so converting helps you pick the right pan at home.
Brakes and clutches
A brake pad of 3 by 4 inches has 12 in², 77.4 cm². A pair of pads per wheel gives 24 in², 155 cm². The braking force depends on the pad area, the pressure and the friction coefficient, so a conversion of area is the first step in comparing American and European brake specifications.
Envelopes and postcards
A number 10 envelope of 4.125 by 9.5 inches has 39.2 in², 253 cm². A postcard of 4 by 6 inches has 24 in², 155 cm². Postal services publish size limits in inches or millimetres, so a mailing from a company in one system to another often needs a conversion.
Cookies, cakes and pizza slices
A 3 inch cookie has a top of 7.07 in², 45.6 cm². An 8 inch cake has 50.3 in², 324 cm². A slice of a 14 inch pizza cut into eight has 19.2 in², 124 cm². Cooking videos use inches, and a viewer abroad can use a “convert in² to cm²” calculation to find the right tin.
Plates and bowls
A 10 inch dinner plate has an area of 78.5 in², 507 cm². A 7 inch side plate 38.5 in², 248 cm². A bowl of 6 inches across has a mouth of 28.3 in², 182 cm². Tableware catalogues from different countries use diameters in the local unit, and areas help compare serving sizes.
Cutting tools and saw blades
A circular saw blade of 7.25 inches has an area of 41.3 in², 266 cm². A table saw blade of 10 inches has 78.5 in², 507 cm². Tool buyers compare blades by diameter, and the area gives a measure of the material in them.
Gaskets and seals
A gasket for a 2 inch pipe flange has an area of about 5 in², 32 cm². A car head gasket covers 150 in², 968 cm². Engineers compute the clamping pressure from bolt force divided by gasket area, so the area in square centimetres is useful for European pressure units.
Electrical panels and boxes
A standard electrical box of 4 by 4 inches has a face of 16 in², 103 cm². A panel of 14 by 20 inches has 280 in², 1,806 cm². Codes limit the number of wires per box volume, and the volume depends on the area and depth, so converting dimensions between systems is part of electrical design.
Rounding
The factor 6.4516 is exact. For most purposes, one decimal in square centimetres is enough. For machining, keep three decimals. Do not round the factor to 6.5 in engineering work, because on 100 in² the error is 5 cm².
Spreadsheet use
Put square inches in column A and write =A2*6.4516 in column B. For the reverse, use =B2/6.4516 or =B2*0.155. Format with one decimal. Add a column of the ratio to check consistency.
Teaching the idea
On graph paper with 1 cm squares, mark a square of 2.54 cm on a side and count the squares: about 6.45. Then compare with a ruler marked in inches. Students see that the area factor is the square of the length factor, which sticks.
Precision in hobby engineering
Model engine builders work with bores of 0.5 to 1.0 inch, areas of 0.2 to 0.8 in², 1.3 to 5.1 cm². Small differences in bore change displacement a lot, so careful conversion of area is a must. A “convert in² to cm²” calculation done with the exact factor avoids errors in the third digit.
Engine bores and displacement
A 350 cubic inch V8 has a bore of 4 inches and a stroke of 3.48 inches. The piston area, 12.57 in², 81.1 cm², multiplied by the stroke of 8.84 cm gives 717 cm³ per cylinder. An eight cylinder engine then has 5.74 litres. The mixture of units shows how conversions run through engine calculations.
Gun and archery targets
A target face of 12 inches across has an area of 113 in², 730 cm². A bullseye of 1 inch has 0.785 in², 5.07 cm². Archery and target shooting societies publish target dimensions in inches or centimetres, and competitors who shoot abroad convert.
Air filters and ventilation
A furnace filter of 16 by 25 inches has an area of 400 in², 2,581 cm², and a filter of 20 by 20 inches 400 in² as well. A larger filter slows the air through it and traps more dust. Manufacturers list the nominal size in inches, the exact size slightly smaller, and the surface area of the pleats many times larger, so a “convert in² to cm²” calculation helps you compare with European filters rated in square centimetres.
Heat sinks and cooling
A computer heat sink with a base of 2 by 2 inches has a contact area of 4 in², 25.8 cm². A graphics card cooler of 10 by 4 inches covers 40 in², 258 cm². Heat transfer depends on area, so specifications in square inches from American brands and in square centimetres from European brands need to be placed on the same scale before you can judge cooling capacity.
Sanding blocks and drywall tools
A drywall sanding sponge of 3 by 5 inches has a face of 15 in², 96.8 cm². A sanding block of 2.75 by 4.5 inches has 12.4 in², 80 cm². DIY users who buy tools from different countries compare sizes by area, and the figure in square centimetres feels natural to those used to metric.
Stickers, decals and labels
A bumper sticker of 3 by 10 inches has 30 in², 194 cm². A laptop decal of 3 by 3 inches has 9 in², 58 cm². Print shops charge by the square inch in the United States and by the square centimetre elsewhere, so comparing two quotes demands a conversion, and a good designer checks both before approving artwork.
Measuring a surface with a grid
To find the area of an irregular shape, place it on a grid of one inch squares, count the whole squares and half of the partial ones. A leaf covering about 12 whole and 8 partial squares has an area near 16 in², 103 cm². Count again on a centimetre grid and you should reach nearly the same figure after a “convert in² to cm²” calculation.
Hydraulic jacks and presses
A shop press with a ram of 2 inch diameter has an area of 3.14 in², 20.3 cm². At 10,000 psi, 690 bar, it exerts 31,400 pounds, 14.2 tonnes force. Hobby presses are sold by the tonnage, but their ram area decides what pressure the pump must reach.
Nozzles and orifices
A nozzle with a diameter of 0.25 inch has an area of 0.049 in², 0.317 cm². A fire hose nozzle of 1.5 inch has 1.77 in², 11.4 cm². Flow depends on the nozzle area and the pressure, so the area in square centimetres can be inserted into metric flow formulae.
Tyre contact patch
A car tyre inflated to 32 psi carries 1,000 pounds on a patch of 31 in², 200 cm². A truck tyre at 100 psi carries 4,000 pounds on 40 in², 258 cm². The area is the weight divided by the pressure, a relation that works the same way in both unit systems.
Paperback books
A mass market paperback of 4.25 by 6.87 inches has a cover of 29.2 in², 188 cm². A trade paperback of 6 by 9 inches has 54 in², 348 cm². Printers set book sizes in inches in the United States and in millimetres elsewhere, and a conversion tells you how much paper a title uses.
Vinyl records
A 12 inch record has a surface of 113 in², 730 cm², and a 7 inch single 38.5 in², 248 cm². The playable groove area is smaller, about 70 per cent of the face. Record collectors compare sleeves, covers and turntable mats in inches, and a “convert in² to cm²” calculation serves anyone who imports from a metric country.
Drums and drumheads
A 14 inch snare drum has a head area of 154 in², 993 cm². A 22 inch bass drum has 380 in², 2,452 cm². Drum shops describe heads by diameter, but their tone depends on the area and tension. Musicians converting from American to European specifications use these figures.
DVD cases and packaging
A standard DVD case of 5.4 by 7.5 inches has a front of 40.5 in², 261 cm². A CD jewel case of 5 by 5.6 inches has 28 in², 181 cm². Packaging designers print covers for different markets, and they must convert the areas between inch and metric templates.
More values for convert in² to cm²
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 in² = 0.64516 cm²
- 0.5 in² = 3.2258 cm²
- 3 in² = 19.3548 cm²
- 4 in² = 25.8064 cm²
- 7 in² = 45.1612 cm²
- 15 in² = 96.774 cm²
- 20 in² = 129.032 cm²
- 75 in² = 483.87 cm²
- 200 in² = 1,290.32 cm²
- 500 in² = 3,225.8 cm²
- 2,000 in² = 12,903.2 cm²
- 10,000 in² = 64,516 cm²
Mistakes when you convert in² to cm²
Using 2.54
That is the linear factor. For area, multiply by 6.4516.
Dividing instead of multiplying
The square centimetre is smaller, so the number grows. If 10 in² became 1.55, you divided.
Forgetting the square
in and in² are different units. Check the exponent on every number you copy.
Quick answers
How many square centimetres in a square inch?
6.4516.
How do I convert in² to cm²?
Multiply by 6.4516.
How many square inches in a square centimetre?
0.155.
What is 10 in² in cm²?
64.5 cm².
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 in² to mm², Convert in² to ft², Convert mm² to cm², Convert m² to cm², Convert cm² to mm², Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. The reverse of this page is Convert cm² to in².
In short, to convert in² to cm² multiply by 6.4516, remember that the factor is the square of 2.54, and keep the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.