Conversion from 100 Square chains to Square decimeters

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 decimeter (dm²)

The square decimetre is a unit of area equal to one hundredth of a square metre, or one hundred square centimetres. It is written dm². It is the area of a square ten centimetres on a side, which is about the size of a palm or a drinks coaster, and it sits in the gap between the square centimetre of small objects and the square metre of rooms.

The decimetre owes its survival to volume rather than to area. A cubic decimetre is exactly one litre, which quietly builds the prefix into the most used volume unit in the world, and a square decimetre is the cross-section of that litre cube. Anyone who can picture a litre carton already knows what a square decimetre looks like: it is the face of the box.

Its one substantial commercial home is the leather trade. Hides are irregular, so they are measured by area rather than by length, and European tanneries, shoe factories and leather goods makers buy and sell in square decimetres. A whole cowhide runs to something like 200 to 250 square decimetres, a lambskin to about 50, and prices, cutting yields and waste allowances are all calculated on that basis. British and American buyers use square feet for the same purpose, and one square foot is 9.29 square decimetres.

Everyday objects land conveniently on it. A sheet of A4 paper is 6.24 square decimetres, a standard floor tile of thirty centimetres is nine, and a large postage stamp is a small fraction of one. Schools use the unit for exactly this reason: it lets a class measure real objects without either very large or very small numbers, and it makes the squaring rule visible, since ten centimetres on a side gives a hundred square centimetres.

Outside those uses it is rare, and for the usual reason. Engineering standardised on prefixes that step by a factor of a thousand, so square millimetres, square metres and square kilometres cover everything in practice. Ten square decimetres is more naturally written as 0.1 square metres, which sorts correctly beside every other figure in a specification.

Converting is straightforward once the squaring is kept in mind. Multiply by a hundred for square centimetres, divide by a hundred for square metres, and remember that the factor between neighbouring units is the square of the factor between the lengths, not the factor itself.

One square decimetre equals 100 square centimetres, 0.01 square metres, or about 15.5 square inches.