|Unit||nearest SI||SI base|
|1 ca||1 m2||1 m2|
|1 a||1 dam2||102 m2|
|1 ha||1 hm2||104 m2|
|100 ha||1 km2||106 m2|
|119.6 sq yard||1 a||102 m2|
|1076.39 sq ft||1 a||102 m2|
Are (symbol a, pronounced /ˈɛər/ or sometimes /ˈɑr/) is a unit of area, equal to 100 square metres (10 m × 10 m), used for measuring land area. It was defined by older forms of the metric system, but is now outside of the modern International System (SI). 
It is commonly used in many countries—in particular, in Indonesia, French-, Portuguese-, Slovakian-, Czech-, Polish-, Dutch- and German-speaking countries—to measure real estate; elsewhere, the square metre is usually used. The are is sometimes used in combination with the centiare, e.g. "10 ares 12 centiares" = 1012 m2. Larger land areas are generally measured in hectares. The decare is commonly used in the former Ottoman countries, usually under local names. Other prefixes for multiples and submultiples of the are are not in common use. There are other local units which are exact multiples of the are, e.g. the Thai rai is equal to 16 a.
The are is the standard unit of measurement for private plots of land (as opposed to large industrial and agricultural properties) in Russia and all the countries of the former Soviet Union. But since the original root word "are" has never been in use in Russian, and only the word "hectare" exists as a unit of land measurement, the Russian word for "are" is "sotka" (ѝотка), which roughly translates as "hundredth". Thus, the Russian language regards the hectare as the "root" unit of measurement, and a "sotka" is essentially a "centihectare", or (1 a × 100 ÷ 100). City dwellers in the former USSR use the term "sotka" to describe the size of their suburban dacha or allotment garden plots or small city parks; country dwellers or wealthy suburban homeowners use it to describe the size of the private yards around their houses, small private orchards, and the like. Hectares are used to describe larger plots of land, such as a factory complex, a collective farm, a university campus, or a nature preserve.
One are is equivalent to:
- 0.0001 km2 (square kilometres)
- 0.01 ha (hectares)
- 1 dam2 = 10 m × 10 m (a square 10 metres on a side)
- 100 m2 (square metres)
- 100 ca (centiares)
- 0.000 038 610 2 square miles (statute)
- 0.024 710 538 international acres
- 0.024 710 439 U.S. survey acres
- approximately 1076.39 square feet
- 0.1 stremma
- 1 E2 m² for a comparison with other areas
- US NIST Reference on SI, Table 7. Other units outside the SI that are currently accepted for use with the SI, subject to further review. Note that this source refers to BIPM SI 7th edition. Reference should be made to BIPM SI 8th edition.