Hectare

Image comparing the hectare (the small blue area at lower left) to other units. The entire yellow square is one square mile.

The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm²), that is, 10,000 square metres (10,000 m²), and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. An acre is about and thus one hectare is about .

St. Enda's GAA ground, in Omagh. The playing field used in Gaelic football and hurling is a little over a hectare in size.

In 1795, when the metric system was introduced, the are was defined as 100 square metres, or one square decametre, and the hectare ("hecto-" + "are") was thus 100 ares or Template:Sfrac km² ( square metres). When the metric system was further rationalised in 1960, resulting in the International System of Units (Template:Encodefirst), the are was not included as a recognised unit. The hectare, however, remains as a non-SI unit accepted for use with the SI and whose use is "expected to continue indefinitely". Though the dekare/decare daa () and are (100 m²) are not officially "accepted for use", they are still used in some contexts.

Description

Comparison of area units

Unit	SI
1 ca	1 m2
1 a	100 m2
1 ha	10,000 m2
100 ha	1 km2
non-SI comparisons
non-SI	metric
0.3861 sq mi	1 km2
2.471 acre	1 ha
	1 ha
1 sq mi	259.0 ha
1 acre	0.4047 ha

Trafalgar Square has an area of about one hectare.

The hectare (), although not a unit of SI, is the only named unit of area that is accepted for use with SI units. The name was coined in French, from the Latin . In practice the hectare is fully derived from the SI, being equivalent to a square hectometre. It is widely used throughout the world for the measurement of large areas of land, and it is the legal unit of measure in domains concerned with land ownership, planning, and management, including law (land deeds), agriculture, forestry, and town planning throughout the European Union, South Africa, New Zealand, Australia, Canada and the United Kingdom. However, the United States and Myanmar (Burma) use the acre instead of the hectare for measuring surface or land area.

In many countries, metrification redefined or clarified existing measures in terms of metric units. The following legacy units of area have been redefined as being equal to one hectare:

• Jerib (Template:Langx) in Iran
• Djerib (Template:Langx) in Turkey
• Gongqing () in China
• Manzana in Argentina
• Bunder in the Netherlands (until 1937)

In Mexico, land area measurements are commonly given as combinations of hectares, ares, and centiares. These are commonly written separated by a hyphen; for example, 1-21-00.26 ha would mean 1 hectare, 21 are, and 0.26 centiare ().

History

The metric system of measurement was first given a legal basis in 1795 by the French Revolutionary government. The law of 18 Germinal, Year III (7 April 1795) defined five units of measure:

• The metre for length
• The are (100 m²) for area [of land]
• The stère (1 m³) for volume of stacked firewood
• The litre (1 dm³) for volumes of liquid
• The gram for mass

In 1960, when the metric system was updated as the International System of Units (SI), the are did not receive international recognition. The International Committee for Weights and Measures (Template:Encodefirst) makes no mention of the are in the 2019 edition of the SI brochure, but classifies the hectare as a "Non-SI unit accepted for use with the International System of Units".

In 1972, the European Economic Community (EEC) passed directive 71/354/EEC, which catalogued the units of measure that might be used within the Community. The units that were catalogued replicated the recommendations of the CGPM, supplemented by a few other units including the are (and implicitly the hectare) whose use was limited to the measurement of land.

Unit family

Definition of a hectare and of an are

The names centiare, deciare, decare and hectare are derived by adding the standard metric prefixes to the original base unit of area, the are.

Decimilliare

The decimilliare (dma, sometimes seen in cadastre area evaluation of real estate plots) is Template:Sfrac are or one square decimetre. Such usage of a double prefix is non-standard. The decimilliare is (100 mm)² or roughly a four-inch-by-four-inch square. (The decimilliare is smaller by approximately 3.1%.)

Centiare

The centiare is one square metre.

Deciare

The deciare (rarely used) is ten square metres.

Are

The are (, ) is a unit of area, equal to 100 square metres (), used for measuring land area. It was defined by older forms of the metric system, but is now outside the modern International System of Units (SI). It is still commonly used in speech to measure real estate, in particular in Indonesia, India, and in various European countries.

In Russian and some other languages of the former Soviet Union, the are is called (сотка: 'a hundred', i.e. 100 m² or Template:Sfrac hectare). It is used to describe the size of suburban dacha or allotment garden plots or small city parks where the hectare would be too large. Many Russian dachas are 6 ares in size (in Russian, ).

Decare

The decare or dekare () is derived from deca and are, and is equal to 10 ares or 1000 square metres. It is used in Norway and in the former Ottoman areas of the Middle East and Bulgaria as a measure of land area. The names of the older land measures of similar size are usually used, redefined as exactly one decare:

• in Greece
• in the Balkans, Israel, Palestine, Jordan, Lebanon, Syria, and Turkey
• in Norway.

Conversions

Metric and British imperial/United States customary comparisons

Unit name	Symbol	Multiple of preceding unit	Fraction of succeeding unit	Length of square side	SI equivalents	British imperial/United States customary equivalents
centiare	ca		0.1 da
deciare	da	10 ca	0.1 a
are	a	10 da	0.1 daa
decare	daa	10 a	0.1 ha
hectare	ha	10 daa	0.01 km2
square kilometre		100 ha

An acre shown inside a hectare for size comparison

The most commonly used units are in bold.

One hectare is also equivalent to:

• 1 square hectometre
• 1.008 (Japan)
• 2.381 (Egypt)
• 6.25 (Thailand)
• 10 or (Middle East)
• 10 (Greece)
• 15 or 0.15

Unicode

The Unicode character , in the CJK Compatibility block, is intended for compatibility with pre-existing East Asian character codes. It is not intended for use in alphabetic contexts. is a combination of (), the Japanese translation of "hectare".

See also

• Conversion of units
• Hectometre
• Order of magnitude

External links

• Official SI website: Table 6. Non-SI units accepted for use with the International System of Units