| Square centimeters (cm²) | Square furlongs (sq fur) |
|---|---|
| 1 Square centimeter | 0.00000000247105381467 sq fur |
| 2 Square centimeters | 0.00000000494210762934 sq fur |
| 3 Square centimeters | 0.00000000741316144401 sq fur |
| 4 Square centimeters | 0.00000000988421525869 sq fur |
| 5 Square centimeters | 0.0000000123552690734 sq fur |
| 10 Square centimeters | 0.0000000247105381467 sq fur |
| 20 Square centimeters | 0.0000000494210762934 sq fur |
| 25 Square centimeters | 0.0000000617763453668 sq fur |
| 50 Square centimeters | 0.000000123552690734 sq fur |
| 100 Square centimeters | 0.000000247105381467 sq fur |
| Reference | Square centimeters (cm²) | Square furlongs (sq fur) |
|---|---|---|
| A sheet of A4 paper | 623.7 cm² | 0.0000015412 sq fur |
| A tennis court | 2608000 cm² | 0.00644451 sq fur |
| A football pitch | 71400000 cm² | 0.176433 sq fur |
| One hectare | 100000000 cm² | 0.247105 sq fur |
| Central Park, New York | 3.41 × 1010 cm² | 84.2629 sq fur |
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 furlong is a unit of area equal to ten acres, or 40,468.6 square metres. Its symbol is sq fur. A furlong is 220 yards, an eighth of a mile, so a square furlong is a hundred square chains and sixty-four of them make a square mile. It is one of the tidiest relationships in the imperial system and one of the least used.
The furlong is older than the acre and gave it its shape. The name means furrow long, and it was the distance an ox team was expected to plough before resting and turning. In the open fields of medieval England a furlong was a block of cultivated strips as well as a length, so the word described a place and a measurement at the same time, and the acre was defined as one furlong by one chain because that was what a day's ploughing produced.
That history explains why the square furlong is arithmetically neat but practically absent. Land was allotted in strips and acres, not in blocks a furlong on a side, so the square form never had a use even when the linear one was in daily service. A surveyor who needed ten acres wrote ten acres, and the square furlong was left as an entry in tables.
The length itself has survived by a peculiar route. Horse racing kept it, and races in Britain, Ireland, the United States, Australia and much of Asia are still described in furlongs: a six-furlong sprint, a mile and a half meaning twelve furlongs. Nothing else in modern life uses the unit, but racing uses it constantly, which keeps the word familiar to people who would struggle to say how long it is.
As an area it is a useful size to picture even so. Ten acres is a small farm, a large public park, about fourteen football pitches, or a city block of generous proportions. New York's Central Park covers roughly eighty-four square furlongs. The unit is large enough that anything measured in it is being described as a place rather than a property.
Converting is cleanest through the acre. Multiply by ten for acres, then by 0.4047 for hectares, or use the direct factor of 4.047 hectares to the square furlong. Going the other way, a hectare is about a quarter of a square furlong, which is close enough for rough comparison of old and new land records.
One square furlong equals 10 acres, 100 square chains, about 40,469 square metres, or about 4.047 hectares.