| Square leagues (sq lea) | Square decameters (dam²) |
|---|---|
| 1 Square league | 233098.92993 dam² |
| 2 Square leagues | 466197.85986 dam² |
| 3 Square leagues | 699296.789791 dam² |
| 4 Square leagues | 932395.719721 dam² |
| 5 Square leagues | 1165494.64965 dam² |
| 10 Square leagues | 2330989.2993 dam² |
| 20 Square leagues | 4661978.5986 dam² |
| 25 Square leagues | 5827473.24826 dam² |
| 50 Square leagues | 11654946.4965 dam² |
| 100 Square leagues | 23309892.993 dam² |
| Reference | Square leagues (sq lea) | Square decameters (dam²) |
|---|---|---|
| A sheet of A4 paper | 0.00000000267569 sq lea | 0.0006237 dam² |
| A tennis court | 0.0000111884 sq lea | 2.608 dam² |
| A football pitch | 0.000306308 sq lea | 71.4 dam² |
| One hectare | 0.000429002 sq lea | 100 dam² |
| Central Park, New York | 0.14629 sq lea | 34100 dam² |
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.
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.