Convert mm² to cm² square millimetres ↔ square centimetres Free Online Secure
Type a value in square millimetres 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 mm² to cm² (square millimetres ↔ square centimetres)
| mm² | cm² |
|---|---|
| 1 | 0.01 |
| 2 | 0.02 |
| 3 | 0.03 |
| 5 | 0.05 |
| 10 | 0.1 |
| 20 | 0.2 |
| 50 | 0.5 |
| 100 | 1 |
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 is a square metre a million square millimetres and not a thousand?
Because area is length multiplied by length. A metre is 1000 millimetres, so a square metre is 1000 × 1000, which is 1,000,000 square millimetres. The same trap catches people with every squared unit: the conversion factor of the length is squared along with the unit.
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.
Culture plates, leaf discs and lab swabs: small areas in square centimetres
Biologists describe the growth surface of a well in square millimetres, the surface of a flask in square centimetres, and the density of cells as so many per square centimetre. A single experiment may move between the two units dozens of times. To convert mm² to cm² you divide by 100, which is the same as moving the decimal point two places to the left. So 320 mm² is 3.2 cm², and 960 mm² is 9.6 cm². This page divides as you type, and the text below shows where the conversion matters in cell culture, plant science and hygiene testing.
Below come the rule, some worked cases, a brief look at each unit, a side by side comparison, a tour of laboratory situations and the slips to avoid. Everything is computed on your own device while you type.
How to convert mm² to cm²: divide by 100
The rule
One square centimetre is exactly 100 square millimetres. To convert mm² to cm², divide the square millimetres by 100, or move the decimal point two places to the left. So 50 mm² is 0.5 cm², 250 mm² is 2.5 cm², 1,200 mm² is 12 cm² and 8 mm² is 0.08 cm². To go back, multiply square centimetres by 100.
Worked examples
A well of a 96 well plate has a growth area of about 32 mm², 0.32 cm². A well of a 24 well plate has 190 mm², 1.9 cm². A well of a 6 well plate has 960 mm², 9.6 cm². When the number has decimals, shift the point as usual: 12.5 mm² is 0.125 cm².
Why two places, not one
A centimetre is 10 millimetres, so a square centimetre is 10 by 10, which is 100. Dividing by 10 gives an answer ten times too big. The mistake comes from using the factor printed on a ruler for an area.
A quick check
The square centimetre is the larger unit, so the number must shrink by two digits. If your “convert mm² to cm²” calculation produced a number with only one digit fewer, you used the length factor.
The square millimetre
A millimetre by a millimetre
The square millimetre is a hundredth of a square centimetre and a millionth of a square metre. It measures wells, wire sections, chip contacts and small lesions. A pinhead has about 1 mm².
Where it appears
Laboratory plastics, cable standards, component data sheets, histology and technical drawings.
The square centimetre
A hundred square millimetres
The square centimetre is the area of a square 1 cm by 1 cm, 0.155 square inches. It is the standard unit for flask surfaces, swab areas, small samples and cell densities.
Where it appears
Biology, medicine, optics, electronics and school geometry. A fingernail is about a square centimetre.
Square millimetre and square centimetre compared
A square centimetre holds a hundred square millimetres. The smaller unit suits wells and contacts, the larger flasks and swabs. In protocols both appear side by side, and a careful scientist converts everything to one unit before doing arithmetic.
The conversion has no rounding. The only trap is the factor: 100, not 10. Writing the unit after every number and keeping a conversion line in the methods section prevents most mistakes.
Where the conversion appears
Cell culture plates and flasks
A T25 flask has a growth area of 25 cm², 2,500 mm². A T75 flask 75 cm², 7,500 mm². A 12 well plate has wells of 380 mm², 3.8 cm². A protocol that says to seed 10,000 cells per cm² puts 3,200 cells in a 96 well plate well of 0.32 cm². A “convert mm² to cm²” calculation gives the figure for each vessel.
Leaf discs and bioassays
A cork borer of 11.3 mm diameter cuts a disc of 100 mm², 1 cm². A smaller one of 6 mm cuts 28.3 mm², 0.283 cm². Plant scientists measure chlorophyll or enzyme activity per leaf area, and the area of a disc is the basis for converting to per square centimetre values.
Surface swabs and hygiene tests
A swab template of 5 by 5 cm covers 25 cm², 2,500 mm². A contact plate has a surface of 25 cm². A result of 8 colonies per plate is 0.32 per cm². Hygiene standards give limits per cm², while a small template or a spot test may be described in mm², so conversions are common.
Microscope slides and cover slips
A cover slip of 22 by 22 mm has 484 mm², 4.84 cm². A larger one of 24 by 50 mm 1,200 mm², 12 cm². A thin tissue section may fill 300 mm², 3 cm², of the slide. Pathologists describe sections in square millimetres, and a cell count per cm² of tissue needs the area converted.
Fingerprints and forensic traces
A fingerprint covers about 200 mm², 2 cm². A full palm print 8,000 mm², 80 cm². A blood spot of 5 mm diameter has 19.6 mm², 0.196 cm². Forensic reports give small areas in mm² and larger ones in cm², so a “convert mm² to cm²” calculation is routine.
Soil cores and sediment samples
A soil corer of 50 mm diameter takes a core with a section of 1,963 mm², 19.6 cm². A sediment core of 100 mm 7,854 mm², 78.5 cm². Soil scientists multiply the section by the depth for volume, and report densities per cm² of surface.
Dust, pollen traps and spore deposition
A sticky pollen trap slide of 24 by 76 mm has 1,824 mm², 18.2 cm². Counting 200 pollen grains gives 11 grains per cm². Aerobiologists count per cm² per day, and individual fields of view are measured in mm², so conversions are part of daily work.
A list to remember
100 mm² is 1 cm², 250 mm² is 2.5 cm², 500 mm² is 5 cm², 1,000 mm² is 10 cm², 5,000 mm² is 50 cm². With these anchors you can judge any figure at a glance, and the converter above gives the exact value of a “convert mm² to cm²” calculation.
Spreadsheet use
Write square millimetres in column A and =A2/100 in column B. For the reverse, use =B2*100. Format with two decimals. A column =B2*C2, with C2 a density per cm², gives the count for each vessel.
Rounding
The factor 100 is exact. Give as many digits as the source: 25 mm² is 0.25 cm², not 0.2500. If a measurement has one significant figure, 30 mm², keep one: 0.3 cm².
Teaching the idea
Draw a square of 10 by 10 mm on graph paper and count the small squares: 100. That is a square centimetre. Students then count squares in a shape and divide by 100 to get its area in cm², which makes the factor visible.
Pipette tips and tubes
A 1.5 ml microtube has an inner section of about 30 mm², 0.3 cm². A 15 ml tube 150 mm², 1.5 cm². A pipette tip opening of 0.5 mm diameter 0.2 mm². Lab suppliers give tube sizes in millimetres and capacity in millilitres, and a conversion is needed to calculate surface to volume ratios.
A mental picture
A square millimetre is a pinhead and a square centimetre a fingernail. One hundred pinheads make a fingernail. If your “convert mm² to cm²” calculation does not fit that picture, repeat the division and count the zeros.
Calculating seeding density for a plate
A protocol asks for 50,000 cells per cm² on a 24 well plate. Each well has 1.9 cm², 190 mm², so you need 95,000 cells per well and 2.28 million for the whole plate. If the protocol is written per mm², 500 per mm², the same number results. A “convert mm² to cm²” calculation makes the two forms interchangeable and spares you a miscalculation that could waste an expensive batch of cells.
Biopsy punches and wound size
A 4 mm biopsy punch removes a disc of 12.6 mm², 0.126 cm². A 6 mm punch 28.3 mm², 0.283 cm². A wound that closes from 200 mm² to 50 mm² has shrunk by 75 per cent, 2 cm² to 0.5 cm². Clinicians measure wounds in mm² or cm², and a conversion allows comparison of records.
Antibody staining and tissue sections
A tissue section of 15 by 10 mm has 150 mm², 1.5 cm², and takes about 150 microlitres of antibody solution at 100 µl per cm². A larger section of 400 mm², 4 cm², takes 400 µl. Technicians scale volumes by area, and the area on the slide is often drawn in millimetres with a graticule, then converted.
Coatings and thin film samples
A thin film sample of 10 by 10 mm has 100 mm², 1 cm². A wafer coupon of 20 by 20 mm 400 mm², 4 cm². Material scientists report film properties per cm², such as resistance per square or current density in milliamps per cm², while the sample size is set in millimetres.
Electrodes and electrochemistry
A working electrode of 3 mm diameter has 7.07 mm², 0.0707 cm². A platinum plate of 10 by 10 mm has 100 mm², 1 cm². Electrochemists report current density in milliamps per cm², so the electrode area, which is often given in mm², must be converted before the result is quoted.
Contact lenses and ophthalmic devices
A soft contact lens of 14.2 mm diameter has an area of 158 mm², 1.58 cm². A scleral lens of 16.5 mm covers 214 mm², 2.14 cm². Eye care specialists describe lens coverage in millimetres, and manufacturers of coating solutions may specify doses per cm² of lens, so a “convert mm² to cm²” calculation is part of product documentation.
Electrostatic and dust sensors
A particle sensor window of 5 by 5 mm has 25 mm², 0.25 cm². A gas sensor membrane of 8 mm diameter 50 mm², 0.5 cm². Specifications give sensitivity per unit area, and the area is stated in whichever unit the maker prefers. A reader comparing two datasheets can use a “convert mm² to cm²” calculation to place both in one unit.
Reading a protocol with two units
A protocol may say to use 200 µl per well of 32 mm² in one step and 0.1 ml per cm² in another. The first is 6.25 µl per mm², the second 1 µl per mm², so the volumes differ by a factor of six. Convert each instruction to one unit before comparing, and note the unit next to every number in your lab book so that a colleague can repeat the work without guessing.
What to keep in mind
A hundred square millimetres make one square centimetre, so every conversion is a shift of two decimal places. Check the direction: going to centimetres the number gets smaller. Check the units on every figure you copy. And when a number will be used in a calculation, keep all its digits until the last step, rounding only for the final report.
Gel electrophoresis and blots
A gel lane 5 mm wide and 40 mm long has 200 mm², 2 cm². A blot membrane of 80 by 60 mm 4,800 mm², 48 cm². Protocols give antibody volumes per cm² of membrane, often 0.1 ml, so the area in cm² is the first number you need. A “convert mm² to cm²” calculation gives it at once.
Bacterial colonies on agar
A petri dish of 90 mm diameter has 6,362 mm², 63.6 cm². Counting 150 colonies gives 2.4 colonies per cm². A spot of 10 mm², 0.1 cm², may hold 10 colonies, so a density of 100 per cm². Microbiology reports use cm² for densities and mm² for individual spots.
Insect wings and morphometrics
A fruit fly wing has about 1.5 mm², 0.015 cm². A honey bee forewing 40 mm², 0.4 cm². A dragonfly wing 600 mm², 6 cm². Entomologists measure wings in square millimetres under a microscope, and compare species in cm² for lecture slides.
Seeds, grains and pollen
A wheat grain has a projected area of about 20 mm², 0.2 cm². A maize kernel 90 mm², 0.9 cm². A bean 140 mm², 1.4 cm². Seed scientists use image analysis to measure projected areas in square millimetres and report mean areas, converting when they compare with weights per cm².
Skin patches and dosage per area
A transdermal patch of 10 cm² delivers a drug at 5 micrograms per hour per cm², 50 µg/h in total. A patch of 600 mm² is 6 cm². Patch labels give area in cm², while the manufacturing drawing uses mm², and the dose depends on the area, so a conversion is built into pharmaceutical specifications.
Dental fillings and enamel
An enamel defect of 3 by 4 mm has 12 mm², 0.12 cm². A filling of 50 mm², 0.5 cm², covers a molar surface of about 100 mm². Dental researchers state areas in square millimetres, and conversions to cm² appear in studies of surface properties of materials.
Corneal and retinal areas
The human cornea has a diameter of about 11.7 mm, an area of 107 mm², 1.07 cm². The retina covers 1,100 mm², 11 cm². The fovea only 1.8 mm², 0.018 cm². Ophthalmology texts use square millimetres, and a conversion lets a reader compare with a lecture in cm².
More values for convert mm² 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 mm² = 0.001 cm²
- 0.5 mm² = 0.005 cm²
- 3 mm² = 0.03 cm²
- 4 mm² = 0.04 cm²
- 7 mm² = 0.07 cm²
- 15 mm² = 0.15 cm²
- 20 mm² = 0.2 cm²
- 75 mm² = 0.75 cm²
- 200 mm² = 2 cm²
- 500 mm² = 5 cm²
- 2,000 mm² = 20 cm²
- 10,000 mm² = 100 cm²
Mistakes when you convert mm² to cm²
Dividing by 10
That is the length factor. For area, divide by 100.
Multiplying instead of dividing
The square centimetre is bigger, so the number shrinks. If 50 mm² became 5,000, you multiplied.
Moving the point one place
Move it two. If you moved it one, the answer is ten times too large.
Quick answers
How many square centimetres in a square millimetre?
0.01.
How do I convert mm² to cm²?
Divide by 100.
What is 250 mm² in cm²?
2.5 cm².
How many square millimetres in a square centimetre?
100.
Is my number sent anywhere?
No, it stays in your browser.
Related pages and a last word
If you work with small areas, these conversions are close at hand: Convert mm² to m², Convert mm² to in², Convert in² to cm², Convert m² to cm², Convert cm² to in², 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 mm².
To sum up: divide by 100 to convert mm² to cm², remember that the factor is the square of 10, and write the unit beside the result. The figure you enter is processed locally, with no account and no upload.