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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
107,639 sq ft 1 ha
1 sq mi 259.0 ha
1 acre 0.4047 ha

The hectare (/ˈhɛktɛər/ or /ˈhɛktɑr/; symbol ha) is a metric unit of area defined as 10,000 square metres (100 m by 100 m), and primarily used in the measurement of land. In 1795, when the metric system was introduced, the "are" was defined as 100 square metres and the hectare ("hecto-" + "are") was thus 100 "ares" or 1100 km2. A hectare of land is about 2.471 acres.

When the metric system was further rationalised in 1960, resulting in the International System of Units (SI), the are was not included as a recognised unit. The hectare is one of the non-SI units accepted for use with the SI units.


The metric system of measure 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:[1]

  • The metre for length
  • The are (100 m2) for area [of land]
  • The stère (1 m3) for volume of stacked firewood[2]
  • The litre (1 dm3) for volumes of liquid
  • The gram for mass

Although the law defined the length of the metre, there was no practical way of accurately measuring the metre (and hence the are) until 1799 when the first standard metre was manufactured and adopted.

The standard metre remained in the custody of successive French governments until 1875 when, under the Convention of the Metre, its supervision passed into international control under the auspices of the General Conference on Weights and Measures (CGPM). At the first meeting of the CGPM in 1889 when a new standard metre, manufactured by Johnson Matthey & Co of London[3] was adopted, the are and hectare were automatically redefined.

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 (CIPM) makes no mention of the are in the current (2006) definition of the SI, but classifies the hectare as a "Non-SI unit accepted for use with the International System of Units"[4]

In 1972, the European Economic Community (EEC) passed directive 71/354/EEC,[5] 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.

The units

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


The centiare (symbol ca) is a synonym for one square metre.


The are (/ˈɛər/[6] or /ˈɑr/;[7] symbol a) 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).[8]

It is commonly used to measure real estate, in particular in Indonesia and in French-, Portuguese-, Slovakian-, Czech-, Polish-, Dutch-, and German-speaking countries as also in India .

In Russia and other former Soviet Union states, the "sotka" (сотка 'hundredth') is identical to the are. 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.


The decare (/ˈdɛkɑr/ or /ˈdɛkər/; symbol daa) is derived from deka, the prefix for 10 and are, and is equal to 10 ares or 1000 square metres. It is used in Norway[9] and in the former Ottoman areas of the Middle East and the Balkans (Bulgaria)[10] as a measure of land area. Instead of the name 'decare', the names of traditional land measures are usually used, redefined as one decare:


The hectare (/ˈhɛktɛər/ or /ˈhɛktɑːr/;[14] symbol ha), although not strictly a unit of SI, is the only named unit of area that is accepted for use within the SI.[15] 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.[16] The United States, Burma[17][18] and to some extent Canada instead use the acre.

Some countries that underwent a general conversion from traditional measurements to metric measurements (e.g. Canada) required a resurvey when units of measure in legal descriptions relating to land were converted to metric units. Others, such as South Africa, published conversion factors which were to be used particularly "when preparing consolidation diagrams by compilation".[19]

In many countries, metrication redefined or clarified existing measures in terms of metric units. (cf. Category:Metricated units) The following legacy units of area have been redefined as being equal to one hectare:[20]


Metric and imperial/US customary comparisons
Unit Symbol Metric equivalents Imperial/US customary equivalents
centiare ca 1 m2 0.01 a 1.19599 sq yd
are a 100 ca 100 m2 0.01 ha 3.95369 perches
decare daa 10 a 1,000 m2 0.1 ha 0.98842 roods
hectare ha 100 a 10,000 m2 0.01 km2 2.471 acres[24]
square kilometre km2 100 ha 1,000,000 m2 0.38610 sq mi

The most commonly used units are in bold.

One hectare is also equivalent to:

Visualising a hectare

Visitors to London can visualize a hectare by visiting Trafalgar Square.[13]

International rugby field

On an international rugby union field the goal lines are up to 100 metres apart. Behind the goal line is the in-goal area (which is also a playing area). This area extends between 10 and 22 metres behind the goal line, giving a maximum length of 144 metres for the playing area. The maximum width of the pitch is 70 metres, giving a maximum playing area of 10,080 square metres or 1.008 hectares.[28]

Statue of Liberty

40°41′21″N 74°2′40″W / 40.68917°N 74.04444°W / 40.68917; -74.04444 (Statue of Liberty)

The Statue of Liberty, a gift from the French people to the American people dedicated on 28 October 1886 to commemorate the hundredth anniversary of the French and American Revolutions, is located on Liberty Island at the entrance to New York Harbor. Its base is built on eighteenth-century fortifications.

The distance between the apex of the bastions in the front of the base to those at the back (where the entrance to the statue is located) is approximately 100 m while the distance between the apexes of the left-hand and right-hand bastions is a little under 100 m. Thus, if a square were to enscribe the bastions, it would have sides of approximately 100 m, giving it an area of one hectare.

Interior of all-weather athletics track

Athletics tracks are found in almost every country of the world. Although many tracks consist of markings on a field of suitable size, where funds permit, specialist all-weather tracks have a rubberized artificial running surface with a grass interior (as shown in the picture and diagram). The perimeter of the inside kerb of the track is a little under 400 metres, as the actual length of the track is measured 300 mm from the inside kerb.[29] The IAAF specifications state that the radius of the kerb is 36.5 m, from which it can be calculated that the area inside the kerb is 1.035 ha.[30]

The soccer field often found inside is normally 105*70 m, that is 0.73 hectares.

See also

Notes and references

External links

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

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