# Ar (unit)

Physical unit
Unit name Ar / Are
Unit symbol ${\ displaystyle \ mathrm {a}}$
Physical quantity (s) Area
Formula symbol ${\ displaystyle A}$
dimension ${\ displaystyle {\ mathsf {L ^ {2}}}}$
In SI units ${\ displaystyle \ mathrm {1 \, a = 100 \; m ^ {2}}}$
In CGS units ${\ displaystyle \ mathrm {1 \, a = 1 \, 000 \, 000 \; cm ^ {2}}}$
Named after Latin ārea , "area, area"
Derived from square meters

The Ar , in Switzerland the Are , is a unit of area in the metric system of 100  m 2 with the unit symbol a (but often not or incorrectly abbreviated: Ar or ar). 100 a equals 1  ha . A square with an area of ​​1 a has an edge length of ten meters, which is why one speaks of a square decameter  ( dam 2 ).

The Ar is not an SI unit; unlike the hectare , it is not even approved for use with the SI.

In the EU and Switzerland, the Ar or the Are is the legal unit for specifying the area of ​​land and parcels.

## history

In 1793, the meter was established in France as the 10 millionth part of the earth quadrant on the Parisian meridian . At the same time, the unit are based on the Latin word ārea (area, free space) for an area of ​​100 m 2 . It was initially the only metric unit of area in use, including its parts and multiples, centiares (1 ca = 1 m 2 ) and hectares (1 ha = 100 a).

In 1868 the unit of measurement was officially introduced in Germany under the name Ar: The corresponding North German order of measurements and weights came into force in 1872 for the entire German Empire.

## Multiples and parts

1 hectare (from "hecto-ar") = 1 ha
= 100 a = 10,000 m 2
= 1 hm 2 = 100 m • 100 m
1 decar (from "Deka-Ar") = 1 daa
= 10 a = 1000 m 2
1 ar
= 1 a = 100 m 2
= 1 dam 2 = 10 m • 10 m
1 centiar
= 0.01 a = 1 m 2
= 1 m 2 = 1 m • 1 m

Except for ares and hectares, these multiples and parts are uncommon in the German-speaking area and are only of historical interest.

The decar is used as a measure of area in Bulgarian agriculture, in Greece ( Stremma ), in Turkey and some countries in the Middle East (metric dunam ).