A decametre or dekametre (American spelling

American English

American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

: dekameter, earlier decameter; symbol dam) is a very rarely used unit

Units of measurement

A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...

 of length

Length

In geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...

 in the metric system

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

, equal to ten metre

Metre

The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

s, the SI

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 base unit

SI base unit

The International System of Units defines seven units of measure as a basic set from which all other SI units are derived. These SI base units and their physical quantities are:* metre for length...

 of length. It can be written in scientific notation

Scientific notation

Scientific notation is a way of writing numbers that are too large or too small to be conveniently written in standard decimal notation. Scientific notation has a number of useful properties and is commonly used in calculators and by scientists, mathematicians, doctors, and engineers.In scientific...

 as (exponential notation), meaning .

This measure is included mostly for completeness. One practical use of the decameter is for altitude of geopotential height

Geopotential height

Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height using the variation of gravity with latitude and elevation. Thus it can be considered a "gravity-adjusted height"...

s in meteorology. Meteorologists also use another seldom encountered SI prefix: hecto-

Hecto

Hecto or hecta is a prefix in the metric system denoting a factor of one hundred. Adopted in 1795, it comes from the Greek hekaton, meaning hundred.It is rarely used, except for certain specific applications:...

 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
  Surface
  In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...
  
   the square decametre (dam²) is a common unit, albeit by the name are
  ARE
  Are, ARE or Åre may refer to: United Arab Emirates using ISO 3166-1 alpha-3 country code*The second-person singular and plural forms of the verb "to be", copula of the English language...
  
   (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 metre
  Square metre
  The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...
  
  s (100 m²).

• For volume
  Volume
  Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
  
  s the cubic decametre (dam³) is also used, 10 m by 10 m by 10 m, equalling 1,000 cubic metre
  Cubic metre
  The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...
  
  s (1,000 m³).

See also

• SI prefix
  SI prefix
  The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
  
  
• deca-
• For length: 1 E+1 m and Orders of magnitude (length)
• For surface: 1 E+2 m² and Orders of magnitude (area)
  Orders of magnitude (area)
  This page is a progressive and labeled list of the SI area orders of magnitude, with certain examples appended to some list objects.-References:...
  
  
• For volume: 1 E+3 m³ and Orders of magnitude (volume)
  Orders of magnitude (volume)
  The pages linked in the right-hand column contain lists of volumes that are of the same order of magnitude . Rows in the table represent increasing powers of a thousand. -Notes:...
  
  
• Conversion of units
  Conversion of units
  Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.- Process :...
  
  , for comparison with other units