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 being 100 square metres and the hectare ('hecto-' + 'are') was thus 100 'ares' or 1/100 km². A hectare of land is about 2.47 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.

History[link]

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 (GCPM). At the first meeting of the GCPM 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 GCPM, supplemented by a few other units including the are (and implicitly the hectare) whose use was limited to the measurement of land.

The units[link]

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

Definition of a hectare and of an are.

Centiare[link]

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

Are[link]

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.

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.

Decare[link]

The decare (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. In the formerly Ottoman area, instead of the name 'decare', the names of traditional land measures are usually used, redefined as one decare:

• Stremma in Greece^[11]
• Dunam, dunum, donum, or dönüm in Israel, Jordan, Lebanon, Syria and Turkey^[12]

Hectare[link]

Trafalgar Square, which has an area of about one hectare.^[13]

The hectare ( /ˈhɛktɛər/ or /ˈhɛktɑːr/;^[14] symbol ha) is widely used throughout the world^[15] and 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^{[citation needed]} and to some extent Canada instead use the acre.^{[citation needed]}

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.^{[citation needed]} Others, such as South Africa, published conversion factors which were to be used particularly when preparing consolidation diagrams by compilation.^[17]

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:^[18]

• Jerib in Iran
• Djerib in Turkey^[19]
• Gong Qing (公顷 - gōngqǐng) in mainland China
• Manzana in Argentina
• Bunder in The Netherlands (until 1937)^[20]

Conversions[link]

The most commonly used units are in bold.

One hectare is also equivalent to:

• 2.4710439 U.S. survey acres
• 15 mǔ or 0.15 qǐng^[21]
• 10 dunam or dönüm (Middle East)^[22]
• 10 stremmata (Greece)
• 6.25 rai (Thai)^[23]
• ≈ 1.008 chō (Japanese)

Visualising a hectare[link]

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

International rugby field[link]

Waikato Stadium – Hamilton, New Zealand The maximum playing area of an international-sized rugby union field is about one hectare 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.[24]

Statue of Liberty[link]

The Statue of Liberty – New York Harbor The Statue of Liberty requires a square of land with an area of one hectare 40°41′21″N 74°2′40″W / 40.68917°N 74.04444°W / 40.68917; -74.04444 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[link]

Hansen Field at Western Illinois University in Macomb, Illinois incorporates an all-weather running track The grass in the centre of a standard athletic track is a little over one hectare in extent 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.[25] 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.[26]

See also[link]

• 1 E+4 m² for further comparisons
• Conversion of units
• Hecto-
• Hectometre
• Order of magnitude

References[link]

External links[link]

Wikimedia Commons has media related to: Hectare

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

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