Conversion from 20 Square chains to Square decameters

Information about the Square chain (sq ch)

The square chain is a unit of area equal to 484 square yards, or 404.686 square metres. Its symbol is sq ch. It is the area of a square one chain on a side, a chain being 22 yards, and ten square chains make exactly one acre. That last relationship is the entire reason the unit exists.

The chain was invented by the English mathematician Edmund Gunter around 1620, and it was a physical object before it was a measurement: a steel chain of one hundred links, 22 yards long, that two people carried across a field. Its length was chosen so that ten square chains would be an acre and eighty chains would be a mile, which let a surveyor work in whole numbers and reach acres by shifting a decimal point.

That was a genuine achievement in an age before decimal calculation. Measurements taken in chains and links could be multiplied together and divided by ten to give acres directly, without the awkward factors of 4840 or 43,560 that the yard and the foot force on the same problem. For three centuries almost every land survey in Britain, Ireland, North America and the colonies was recorded this way.

The consequences outlived the tool. American public land records are written in chains, so deeds and plats still describe boundaries as so many chains and links, and anyone tracing an old title has to convert. Wildland firefighting in the United States measures fire line and fire perimeter in chains to this day, because the unit was already embedded in forestry practice when the agencies were formed.

One familiar object preserves the length exactly. A cricket pitch is one chain from wicket to wicket, twenty-two yards, which is why that number appears in the laws of the game and nowhere else in modern sport. Anyone who can picture a cricket pitch can picture a chain, and a square chain is that length squared, roughly a tenth of an acre or a large suburban garden.

For conversion, the useful facts are that ten square chains make an acre and that one square chain is about 405 square metres, so a hectare is nearly twenty-five square chains. Old surveys quoting areas in chains convert cleanly to acres and only awkwardly to metric, which is a good reason to do the acre step first.

One square chain equals 484 square yards, 0.1 acres, about 404.686 square metres, or about 0.0405 hectares.

Information about the Square decameter (dam²)

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.