Comparison of Area units Unit SI 1 ca 1 m2 1 a 100 m2 1 ha 10000 m2 100 ha 1 km2 non-SI comparisons non-SI metric 0.3861 sq mi 1 km2 2.471 acre 1 ha 107639 sq ft 1 ha 1 sq mi 259.0 ha 1 acre 0.4047 ha

The hectare ( /hktr/ or /hktr/; symbol ha) is a unit of area defined as 10000 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.

When the metric system was rationalised in 1960 with the introduction of the International System of Units (SI) international recognition of the are was withdrawn though the hectare continued to be recognised as a "unit of measure that may be used with SI". Contents 1 History 2 The units 2.1 Centiare 2.2 Deciare 2.3 Are 2.4 Decare 2.5 Hectare 3 Conversions 4 Visualising a hectare 4.1 International rugby field 4.2 Statue of Liberty 4.3 Interior of all-weather athletics track 5 See also 6 References 7 External links History

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 stre (1 m3) for volume of stacked firewood2 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 London3 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

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

The centiare (symbol ca) is a synonym for one square metre. Deciare The deciare is a synonym for ten square metres. Are The are ( /r/6 or /r/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" ( '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 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 only used in a few countries including Norway9 and Bulgaria.10 The following legacy units of land measure have been defined as being equal to one decare: Stremma in Greece11 Dunam dunum donum or dnm in Israel Jordan Lebanon Syria and Turkey12 Hectare Trafalgar Square which has an area of about one hectare.13 The hectare ( /hktr/ or /hktr/14; symbol ha) is widely used throughout the world15 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 and to some extent Canada instead use the Imperial measurement unit of area the acre (1 acre / 0.404686 hectares)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 counties the advent of metrication has meant that national units of measure were either redefined or clarified in terms of metric units. The following legacy units of area have been redefined as being equal to one hectare:18 Jerib in Iran Djerib in Turkey Gong qng in mainland China Manzana in Argentina Bunder in The Netherlands (until 1937)19 Conversions Metric and Imperial Comparisons Units Symbol Metric Equivalents Imperial 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 1000 m2 0.1 ha 0.98842 roods hectare ha 100 a 10000 m2 0.01 km2 2.47105 acres square kilometre km2 100 ha 1000000 m2 0.38610 sq mi The most commonly used units are in bold. One hectare is also equivalent to: 2.4710439 U.S. survey acres 15 m or 0.15 qng 20 10 dunam or dnm (Middle East) 10 stremmata (Greece) 6.25 rai (Thai)21 1.008 ch (Japanese) Visualising a hectare Visitors to London can visualize a hectare by visiting Trafalgar square. International rugby field 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 10080 square metres or 1.008 hectares.22 Statue of Liberty The Statue of Liberty New York Harbour The Statue of Liberty requires a square of land with an area of one hectare 404121N 74240W / 40.68917N 74.04444W / 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 Harbour. Its base is modelled 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 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 an 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.23 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.24 See also 1 E+4 m for further comparisons Conversion of units Hecto- Hectometre Order of magnitude References "La loi du 18 Germinal an 3 (The law of 18 Germanial year 3)  la mesure rpublicaine de superficie pour les terrains gale un carr de dix mtres de ct ". Le CIV (Centre d'Instruction de Vilgnis) - Forum des Anciens. http://aviatechno.free.fr/unites/nouveausys.php. Retrieved 2010-03-02.  Thierry Thomasset. "Le stre" (in French). Tout sur les units de mesure All the units of measure. Universit de Technologie de Compigne. http://www.utc.fr/tthomass/Themes/Unites/unites/infos/stere/Le%20stere.pdf. Retrieved 2011-03-21.  F J Smith. "Standard Kilogram Weights - A Story of Precision Fabrication". Platinum Metals Rev. 1973 17 (2). http://www.platinummetalsreview.com/pdf/pmr-v17-i2-066-068.pdf. Retrieved 2010-03-05.  "SI brochure (Chapter 4; Table 6)". International Bureau of Weights and Measures. 2006. http://www.bipm.org/en/si/sibrochure/chapter4/table6.html. 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)". http://eur-lex.europa.eu/Notice.domodedbl&langen&lng1ennl&lng2dadeelenesfritnlpt&val22924:cs&page1&hwords. Retrieved 2009-02-07.  http://www.macmillandictionary.com/dictionary/american/are7 "are". Oxford Dictionaries. http://oxforddictionaries.com/view/entry/mengb0038720rskeysLRO50&result2#mengb0038720. Retrieved 2010-12-24.  "SI brochure (8th edition)". BIPM. March 2006. http://www.bipm.org/en/si/sibrochure/.  "Decrease in total grain yield". Grain and oil seeds area and production 2002. Statistics Norway. http://www.ssb.no/kornen/arkiv/art-2003-03-19-01-en.html. Retrieved 2010-11-16.  "Market of agricultural land in Bulgaria". BNR Radio Bulgaria. 5 October 2010. http://www.bnr.bg/sites/en/Economy/Pages/0510Marketofagriculturalland.aspx. Retrieved 2010-11-16.  (Dictionary of Modern Greek) 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 9780714654263. http://books.google.com/booksidekQOAAAAQAAJ&dqEl-Eini+%22Mandated+Landscape%22&printsecfrontcover&sourcebl&otsNqqy5AZ68a&sig7a4faV6nF9rSonfla0pC5wCGZA&hlen&eixPzSfHgJqXhtgelJWQBw&saX&oibookresult&ctresult&resnum1#PPR23M1. 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. http://www.official-documents.gov.uk/document/hc0506/hc16/1631/1631.pdf. Retrieved 2010-02-24.  "hectare". Oxford Dictionaries. http://oxforddictionaries.com/view/entry/mengb0370830#mengb0370830. Retrieved 2010-12-24.  Bureau international des poids et mesures (2006). The International System of Units (SI). 8th ed.. http://www.bipm.org/utils/common/pdf/sibrochure8en.pdf. 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". http://eur-lex.europa.eu/LexUriServ/LexUriServ.douriCONSLEG:1980L0181:20090527:EN:PDF. Retrieved 2010-01-29.  "Instructions for the Conversions of Areas to Metric". Law Society of South Africa. 2007-11. http://www.lawsoc.co.za/webs/surveyorgeneral/200711areaconversion.doc. Retrieved 2011-01-21.  Britannica unit of measurement accessed 2009-10-30 Oscar van Vlijmen (11 September 2006). "Oppervlakte Area" (in Dutch). Eenheden constanten en conversies Units constants and conversion. http://home.kpn.nl/vanadovv/Opp.html. Retrieved 2011-01-15.  "Chinese Measurements - Units of Area". On-line Chinese Tools. http://www.mandarintools.com/measures.html. Retrieved 2010-12-24.  "Thailand Property Conversion". Siam Legal (Thailand) Co. Ltd. http://www.siam-legal.com/realestate/thailand-convert-rai.php. Retrieved 2010-12-24.  "Law 1 - The Ground". Laws of the Game - Rugby Union 2010. International Rugby Board (IRB). http://www.irblaws.com/EN/laws/2/1/2/before-the-match/the-ground/the-plan/#clause2. Retrieved 2010-12-19.  "IAAF 400 Metre Standard Track Marking Plan". IAAF. 2008. http://www.iaaf.org/mm/Document/Competitions/TechnicalArea/04/63/95/20081202044225httppostedfileFig2.2.1.6aMarkingOutdoor7462.pdf. Retrieved 2010-09-28.  This is a standard high school problem in geometry External links Wikimedia Commons has media related to: Hectare Official SI website: Table 6. 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