Conversion from 3 Deciares to Square leagues

Information about the Deciare (da)

The deciare is a unit of area equal to one tenth of an are, or ten square metres. Its symbol is da. It completes the decimal ladder that the French metric law of 1795 built around the are, alongside the centiare below it and the hectare above, but unlike either of those it never found a job and is today the least used member of the family.

Ten square metres is an easily pictured quantity. It is a small bathroom, a single bedroom in a modest flat, or four fifths of a car parking space. It is the floor of a garden shed, the area a market trader is allotted at a fair, or the footprint of a large dining table with chairs pushed back. Nothing about the size is obscure; only the name is.

The reason it failed is structural. Land registration adopted a three-column system running hectare, are and centiare, each step a factor of one hundred, which mirrors how areas actually behave: squaring a tenfold change in length produces a hundredfold change in area. A tenth of an are sits between two columns and belongs to neither, so no register ever needed a place for it.

Its symbol makes matters worse. In the International System, da is the prefix symbol for deca, so a reader meeting da in a technical document is far more likely to take it as the start of a compound like dam or daN than as a unit in its own right. The decare, ten times larger, is written daa, which does nothing to help.

Where the quantity does need naming, ordinary metric notation handles it without effort. Ten square metres is written 10 m², which is shorter than one deciare, needs no explanation, and sorts correctly beside every other figure on a plan or in a contract.

The unit therefore survives almost entirely in conversion tables and in teaching material that runs through the complete prefix ladder. Encountering it in a real document usually means the document is old, translated from an older source, or reproducing a table rather than making a measurement, and converting it to square metres at once is the safe response.

One deciare equals 10 square metres, 0.1 ares, 0.001 hectares, or about 107.6 square feet.

Information about the Square league (sq lea)

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.