| Square centimeters (cm²) | Square chains (sq ch) |
|---|---|
| 1 Square centimeter | 0.000000247105381467 sq ch |
| 2 Square centimeters | 0.000000494210762934 sq ch |
| 3 Square centimeters | 0.000000741316144401 sq ch |
| 4 Square centimeters | 0.000000988421525869 sq ch |
| 5 Square centimeters | 0.00000123552690734 sq ch |
| 10 Square centimeters | 0.00000247105381467 sq ch |
| 20 Square centimeters | 0.00000494210762934 sq ch |
| 25 Square centimeters | 0.00000617763453668 sq ch |
| 50 Square centimeters | 0.0000123552690734 sq ch |
| 100 Square centimeters | 0.0000247105381467 sq ch |
| Reference | Square centimeters (cm²) | Square chains (sq ch) |
|---|---|---|
| A sheet of A4 paper | 623.7 cm² | 0.00015412 sq ch |
| A tennis court | 2608000 cm² | 0.644451 sq ch |
| A football pitch | 71400000 cm² | 17.6433 sq ch |
| One hectare | 100000000 cm² | 24.7105 sq ch |
| Central Park, New York | 3.41 × 1010 cm² | 8426.29 sq ch |
The square centimetre is a unit of area equal to one ten-thousandth of a square metre, written cm². It is the area of a square one centimetre on a side, and it contains one hundred square millimetres. It is the working unit for anything the size of a hand or smaller: wounds, printed circuits, laboratory cultures, sensor chips and postage stamps.
The arithmetic catches people out. Because area scales with the square of length, one hundred square centimetres make a square decimetre and ten thousand make a square metre, not one hundred. A square ten centimetres on a side is 100 cm², and doubling its side to twenty centimetres gives 400 cm², not 200. Nearly every mistake made with this unit comes from applying the linear factor instead of the squared one.
Medicine measures skin in it. Wounds, ulcers, burns and skin lesions are recorded in square centimetres so that healing can be tracked as a shrinking number over weeks, and dermatological treatments are dosed by the area treated. A typical adult palm covers roughly 100 square centimetres, which is why the palm is used as a rough field estimate of burn extent.
Laboratories rely on it for cell culture. Flasks are named by their growth surface, so a T25 offers 25 square centimetres and a T75 offers 75, and cell densities are counted per square centimetre. Photovoltaic research reports efficiency on cells of exactly one square centimetre, precisely so that results from different laboratories describe the same thing.
Engineering uses it for pressure in some traditions. The kilogram-force per square centimetre, close to one atmosphere, is still printed on tyre gauges, pressure vessels and hydraulic equipment in Japan, Korea and parts of eastern Europe, and it survives because the number it produces is conveniently near the values people already knew. Printed circuit boards are quoted and priced by the square centimetre for the same practical reason.
Against the imperial system it faces the square inch, which is 6.4516 square centimetres exactly. That factor comes straight from the inch being defined as exactly 2.54 centimetres, so unlike most imperial conversions this one is not an approximation, merely an awkward number.
One square centimetre equals 100 square millimetres, 0.0001 square metres, or about 0.155 square inches.
The square chain is a unit of area equal to 484 square yards, or 404.686 square metres. Its symbol is sq ch. It is the area of a square one chain on a side, a chain being 22 yards, and ten square chains make exactly one acre. That last relationship is the entire reason the unit exists.
The chain was invented by the English mathematician Edmund Gunter around 1620, and it was a physical object before it was a measurement: a steel chain of one hundred links, 22 yards long, that two people carried across a field. Its length was chosen so that ten square chains would be an acre and eighty chains would be a mile, which let a surveyor work in whole numbers and reach acres by shifting a decimal point.
That was a genuine achievement in an age before decimal calculation. Measurements taken in chains and links could be multiplied together and divided by ten to give acres directly, without the awkward factors of 4840 or 43,560 that the yard and the foot force on the same problem. For three centuries almost every land survey in Britain, Ireland, North America and the colonies was recorded this way.
The consequences outlived the tool. American public land records are written in chains, so deeds and plats still describe boundaries as so many chains and links, and anyone tracing an old title has to convert. Wildland firefighting in the United States measures fire line and fire perimeter in chains to this day, because the unit was already embedded in forestry practice when the agencies were formed.
One familiar object preserves the length exactly. A cricket pitch is one chain from wicket to wicket, twenty-two yards, which is why that number appears in the laws of the game and nowhere else in modern sport. Anyone who can picture a cricket pitch can picture a chain, and a square chain is that length squared, roughly a tenth of an acre or a large suburban garden.
For conversion, the useful facts are that ten square chains make an acre and that one square chain is about 405 square metres, so a hectare is nearly twenty-five square chains. Old surveys quoting areas in chains convert cleanly to acres and only awkwardly to metric, which is a good reason to do the acre step first.
One square chain equals 484 square yards, 0.1 acres, about 404.686 square metres, or about 0.0405 hectares.