A decametre or dekametre (American spelling: dekameter, earlier decameter; symbol dam, sometimes Dm or dkm) is a very rarely used unit of length in the metric system, equal to ten metres, the SI base unit of length. It can be written in scientific notation as 1 E+1 m (exponential notation), meaning 10 × 1 m.
This measure is included mostly for completeness. One practical use of the decameter is for altitude of geopotential heights in meteorology. Meteorologists also use another seldom encountered SI prefix: hecto- in hectopascal (hPa). The volumetric form (see below) cubic decametre is convenient for describing large volumes of water such as in rivers and lakes.
- For surface the square decametre (dam2) is a common unit, albeit by the name are (a). The are is a measurement of area the size of 1 decametre by 1 decametre — the square decametre — 10 metres by 10 metres, equalling 100 square metres (100 m2).
- For volumes the cubic decametre (dam3) is also used, 10 m by 10 m by 10 m, equalling 1,000 cubic metres (1,000 m3).
See also