| Square decameters (dam²) | Square meters (m²) |
|---|---|
| 1 Square decameter | 100 m² |
| 2 Square decameters | 200 m² |
| 3 Square decameters | 300 m² |
| 4 Square decameters | 400 m² |
| 5 Square decameters | 500 m² |
| 10 Square decameters | 1000 m² |
| 20 Square decameters | 2000 m² |
| 25 Square decameters | 2500 m² |
| 50 Square decameters | 5000 m² |
| 100 Square decameters | 10000 m² |
| Reference | Square decameters (dam²) | Square meters (m²) |
|---|---|---|
| A sheet of A4 paper | 0.0006237 dam² | 0.06237 m² |
| A tennis court | 2.608 dam² | 260.8 m² |
| A football pitch | 71.4 dam² | 7140 m² |
| One hectare | 100 dam² | 10000 m² |
| Central Park, New York | 34100 dam² | 3410000 m² |
The square decametre is a unit of area equal to one hundred square metres. It is written dam², and it is the area of a square ten metres on a side, since a decametre is ten metres. It is exactly the same quantity as the are, and the choice between the two names is a choice between strict metric grammar and two centuries of habit.
The International System is built from coherent units, meaning every derived unit is a product or quotient of base units with no extra factors. Squaring a prefixed length gives a perfectly coherent area, so the square decametre needs no special permission to exist. The are, by contrast, is listed as a non-SI unit accepted for use with the SI, tolerated for land measurement rather than derived from anything.
Despite that formal advantage, the square decametre lost decisively. The are was already in every French land register when the modern system was codified, and a register does not change its columns for a matter of notation. The result is that the correct SI form is almost never written, and its accepted non-SI equivalent is what appears on deeds across half of Europe.
The quantity itself is a useful one to be able to picture, whichever name is used. A hundred square metres is a square ten metres on a side: a generous garden, the ground floor of a small house, a market stall pitch, or a large classroom. It is the last area a person can pace out accurately without instruments, and it is the natural size for describing a plot rather than a field.
Where the symbol does appear, the exponent must be read carefully. The string dam already means decametre, a length, so dam² and dam differ by an entire dimension, and a dropped superscript turns an area into a distance. Software that strips formatting from tables is a common cause of exactly that error.
For any practical purpose, converting is the right response. Multiply by a hundred for square metres, divide by a hundred for hectares, and the resulting figure will match whatever else is on the page. One square decametre is one are, and both are one hundred square metres, so nothing is lost in either direction.
One square decametre equals 100 square metres, 1 are, 0.01 hectares, or about 1076.4 square feet.
The square metre is the SI unit of area, written m². It is the area of a square whose sides each measure one metre, and because the metre is a base unit, every other area unit in the system is derived from it by squaring a length. It is the unit in which most of the world buys homes, specifies materials and describes land.
Property is its largest everyday use. Outside the United States and, in part, the United Kingdom, dwellings are advertised, taxed and compared by their floor area in square metres, and price per square metre is the standard way of comparing one district with another. A modest one-bedroom flat runs to about 45 square metres, a family house between 100 and 150, and a single parking space takes up roughly 12.5.
Materials are sold and specified by the square metre because coverage, not volume, is what a builder needs to know. A litre of emulsion paint covers about ten square metres, floor tiles and laminate are priced by the square metre, and insulation is rated by its thermal resistance per square metre. Paper carries its own version of the same idea: the weight of a sheet stock is given in grams per square metre, so 80 g/m² office paper and 300 g/m² card are compared on one scale.
Physics uses the square metre as the denominator of almost every flux. Solar irradiance at the earth's surface peaks near 1000 watts per square metre, which is the figure solar panels are rated against. Pressure is force per square metre, and one newton per square metre is one pascal by definition. Heat loss through a wall is quoted in watts per square metre per kelvin, and sound intensity in watts per square metre.
Medicine uses it for the human body. An adult's skin covers between 1.6 and 2.0 square metres, and that figure is calculated for each patient before chemotherapy, because many drug doses are prescribed in milligrams per square metre rather than per kilogram. Burn severity is assessed as the percentage of body surface affected, using the same underlying measurement.
Where imperial units survive, the square foot competes directly with it. American and British commercial property is still let by the square foot, and one square metre is 10.76 square feet, which is why converted figures rarely come out round. Land at a larger scale moves to the hectare, equal to 10,000 square metres, and then to the square kilometre.
One square metre equals 10,000 square centimetres, about 10.764 square feet, about 1.196 square yards, or 0.0001 hectares.