|Unit system||SI derived unit|
|In SI base units:||1 ha = 104 m2|
|1 ca||1 m2|
|1 a||100 m2|
|1 ha||10,000 m2|
|100 ha||1 km2|
|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 (// or //; symbol ha) is a non-SI metric system unit of area equal to 1 square hectometre (1 hm2) or 10,000 square metres (104 m2) and primarily used in the measurement of land. An acre is about 0.4047 hectare and one hectare contains about 2.47 acres.
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 1⁄100 km2. 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, however, remains as a non-SI unit accepted for use with the SI units, mentioned in Section 4.1 of the SI Brochure as a unit whose use is "expected to continue indefinitely".
- 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
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 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"
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.
The centiare (symbol ca) is a synonym for one square metre.
The deciare is ten square meters
The are (// or //; 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).
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 (// or //; 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 and in the former Ottoman areas of the Middle East and the Balkans (Bulgaria) as a measure of land area. Instead of the name 'decare', the names of traditional land measures are usually used, redefined as one decare:
- Stremma in Greece
- Dunam, dunum, donum, or dönüm in Israel, Jordan, Lebanon, Syria and Turkey
- Mål is sometimes used for decare in Norway, from the old measure of about the same area.
The hectare (// or //; symbol ha), although not strictly a unit of SI, is the only named unit of area that is accepted for use within the SI. 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. The United States, Burma 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".
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:
- Jerib in Iran
- Djerib in Turkey
- Gong Qing (公顷 - gōngqǐng) in mainland China
- Manzana in Argentina
- Bunder in The Netherlands (until 1937)
|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|
|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:
- 15 mǔ or 0.15 qǐng
- 10 dunam or dönüm (Middle East)
- 10 stremmata (Greece)
- 6.25 rai (Thai)
- ≈ 1.008 chō (Japanese)
- ≈ 2.381 feddan (Egypt)
Visualising a hectare
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.
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. 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.
The soccer field often found inside is normally 105*70 m, that is 0.73 hectares.
Notes and references
- BIPM (2014). "SI Brochure, Table 6". Retrieved 17 November 2014.
- "La loi du 18 Germinal an 3 « la mesure [républicaine] de superficie pour les terrains, égale à un carré de dix mètres de côté »" [The law of 18 Germanial year 3 "The [Republican] measure of land area equivalent to a ten-meter square"] (in French). Le CIV (Centre d'Instruction de Vilgénis) – Forum des Anciens. Retrieved 2010-03-02.
- Thierry Thomasset. "Le stère". Tout sur les unités de mesure [All the units of measure] (in French). Université de Technologie de Compiègne. Retrieved 2011-03-21.
- F J Smith. "Standard Kilogram Weights – A Story of Precision Fabrication". Platinum Metals Rev., 1973, 17, (2). Retrieved 2010-03-05.
- "SI brochure (Chapter 4; Table 6)". International Bureau of Weights and Measures. 2006. Retrieved 2010-03-05.
- "Council Directive of 18 October 1971 on the approximation of laws of the member states relating to units of measurement, (71/354/EEC)". Retrieved 2009-02-07.
- "are – definition. American English definition of are by Macmillan Dictionary". Macmillandictionary.com. Retrieved 2012-05-20.
- "are". Oxford Dictionaries. Retrieved 2010-12-24.
- "SI brochure (8th edition)". BIPM. March 2006.
- "Decrease in total grain yield". Grain and oil seeds, area and production, 2002. Statistics Norway. Retrieved 2010-11-16.
- "Market of agricultural land in Bulgaria". BNR Radio Bulgaria. 5 October 2010. Retrieved 2010-11-16.
- Λεξικό της κοινής Νεοελληνικής (Dictionary of Modern Greek), Ινστιτούτο Νεοελληνικών Σπουδών, Θεσσαλονίκη, 1998. ISBN 960-231-085-5
- El-Eini, Roza I.M. (2006). "Currency and Measures". Mandated landscape: British imperial rule in Palestine, 1929–1948. Routledge. p. xxiii. ISBN 978-0-7146-5426-3. Retrieved 2009-05-05.
- "DEPARTMENT FOR ENVIRONMENT, FOOD AND RURAL AFFAIRS, AND RURAL PAYMENTS AGENCY; The Delays in Administering the 2005 Single Payment Scheme in England". National Audit Office. 2006-10-18. p. 27. Retrieved 2010-02-24.
- "hectare". Oxford Dictionaries. Retrieved 2010-12-24.
- Bureau international des poids et mesures (2006). "The International System of Units (SI)". 8th ed. Retrieved 2008-02-13. Chapter 5.
- The Council of the European Communities (2009-05-27). "Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC". Retrieved 2010-01-29.
- "Appendix G – Weights and Measures". The World Factbook. CIA. 2006. Retrieved 8 August 2006.
- MYA/01/008 Agriculture Sectore Review, Working Paper No. 6 - Agroindustry in Myanmar
- "Instructions for the Conversions of Areas to Metric". Law Society of South Africa. November 2007. Retrieved 2011-01-21.
- Britannica, unit of measurement, accessed 2009-10-30
- Chisholm, Hugh (1911). The Encyclopædia britannica: a dictionary of arts, sciences, literature and general information. The Encyclopædia britannica company. p. 442. Retrieved 15 March 2012.
- Oscar van Vlijmen (11 September 2006). "Oppervlakte" [Area]. Eenheden, constanten en conversies [Units, constants and conversion] (in Dutch). Retrieved 2011-01-15.
- Jacob de Gelder (1824). Allereerste Gronden der Cijferkunst [Introduction to Numeracy] (in Dutch). 's Gravenhage and Amsterdam: de Gebroeders van Cleef. p. 156. Retrieved 19 September 2012.
- 2.4710439 U.S. survey acres or 2.4710538 international acres
- "Chinese Measurements – Units of Area". On-line Chinese Tools. Retrieved 24 December 2010.
- François Cardarelli (2003). Encyclopaedia of scientific units, weights, and measures: their SI equivalences and origins. London, Berlin and Heidelberg: Springer Verlag. p. 97. ISBN 1-85233-682-X. Retrieved 29 March 2011.
- "Thailand Property Conversion". Siam Legal (Thailand) Co., Ltd. Retrieved 2010-12-24.
- "Law 1 – The Ground". Laws of the Game – Rugby Union 2010. International Rugby Board (IRB). Retrieved 2010-12-19.
- "IAAF 400 Metre Standard Track Marking Plan". IAAF. 2008. p. 35. Retrieved 2013-02-11.
- This is a standard high school problem in geometry
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