| Square centimeters (cm²) | Square leagues (sq lea) |
|---|---|
| 1 Square centimeter | 4.2900239838 × 10-12 sq lea |
| 2 Square centimeters | 8.58004796761 × 10-12 sq lea |
| 3 Square centimeters | 1.28700719514 × 10-11 sq lea |
| 4 Square centimeters | 1.71600959352 × 10-11 sq lea |
| 5 Square centimeters | 2.1450119919 × 10-11 sq lea |
| 10 Square centimeters | 4.2900239838 × 10-11 sq lea |
| 20 Square centimeters | 8.58004796761 × 10-11 sq lea |
| 25 Square centimeters | 1.07250599595 × 10-10 sq lea |
| 50 Square centimeters | 2.1450119919 × 10-10 sq lea |
| 100 Square centimeters | 4.2900239838 × 10-10 sq lea |
| Reference | Square centimeters (cm²) | Square leagues (sq lea) |
|---|---|---|
| A sheet of A4 paper | 623.7 cm² | 0.00000000267569 sq lea |
| A tennis court | 2608000 cm² | 0.0000111884 sq lea |
| A football pitch | 71400000 cm² | 0.000306308 sq lea |
| One hectare | 100000000 cm² | 0.000429002 sq lea |
| Central Park, New York | 3.41 × 1010 cm² | 0.14629 sq lea |
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 league is a unit of area equal to nine square miles, or about 23.31 square kilometres. Its symbol is sq lea. A league here is three statute miles, 4828.032 metres, so a square league is a square three miles on a side and holds 5760 acres. It is an obsolete unit that survives in historical land records and in the names of places whose boundaries were drawn with it.
The league began as a measure of time as much as of distance. In Roman and medieval usage it was roughly the distance a person could walk in an hour, which meant that its length varied with the terrain, the country and the century. English practice eventually fixed it at three miles, but the French lieue, the Spanish legua and the Portuguese légua were all different, and none of them agreed with each other.
That variation matters for anyone reading old documents. A grant recorded in leagues cannot be converted safely without knowing which league the surveyor meant. Spanish colonial grants in Texas and California used the legua based on the vara, giving a league of about 4428 acres rather than 5760, and county boundaries in parts of Texas still follow lines that were laid out on that basis.
At sea the unit lasted longer than on land. The marine league of three nautical miles gave the old three-mile territorial limit its name, and charts and treaties used it into the nineteenth century. The modern territorial sea of twelve nautical miles replaced it, but the phrase survives in older law and in fiction, where a journey of twenty thousand leagues describes distance travelled and not depth reached.
As a plain quantity, a square league is a substantial piece of country: nine square miles is a large parish, a small city, or a block of farmland that would take an hour to walk across. It is the scale at which land stops being a holding and becomes a district, which is precisely why grants of that size were made to found settlements rather than farms.
For conversion, nine square miles, 23.31 square kilometres or 2331 hectares all describe the same area. Any figure taken from a historical source should be checked against the definition in use at the time, because the same word can differ by thirty per cent between two neighbouring jurisdictions.
One square league equals 9 square miles, 5760 acres, about 23.31 square kilometres, or about 2331 hectares.