Conversion from 50 Square decimeters to Centiares

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.

Information about the Centiare (ca)

The centiare is a unit of area equal to one hundredth of an are, which makes it exactly one square metre. Its symbol is ca. It is the only unit in common use that is an exact duplicate of another under a different name, and the reason it exists at all is a matter of bookkeeping rather than of measurement.

When the French metric law of 1795 established the are as the decimal unit of land, it created a full ladder around it: the hectare above and the centiare below. Land registries then adopted a three-column format, recording every parcel as so many hectares, so many ares and so many centiares. The last column needed a name, and the square metre, though identical, did not fit the pattern.

That format is still in force. French, Belgian, Luxembourgish and Dutch land registers write parcel areas as three numbers in sequence, so 1 ha 25 a 30 ca means 12,530 square metres. The middle and last figures never exceed 99, which makes the notation self-checking: a value like 1 ha 130 a is malformed and signals a transcription error before anyone has to do arithmetic.

Reading it is a matter of place value. Each hectare is 10,000 square metres, each are is 100, and each centiare is one, so the three columns simply spell out a number in base one hundred. A notary's figure of 0 ha 04 a 62 ca is 462 square metres, and a surveyor's plan showing the same plot would print 462 m² without further comment.

Outside the land registry the centiare has no life. Nobody specifies a floor, a wall or a plot of ground in centiares when the square metre says the same thing with a symbol everyone recognises, and no branch of science or engineering has ever adopted it. It is a unit that exists to fill a column.

The one hazard is the symbol. In many documents ca is an abbreviation for the Latin circa, meaning approximately, so a figure that reads ca 400 could mean 400 centiares or about 400 of something else entirely. In land records the position of the number resolves it; in running text, converting to square metres removes the ambiguity for good.

One centiare equals exactly 1 square metre, 0.01 ares, or about 10.764 square feet.