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The hectare (/ˈhɛktɛər, -tɑːr/; SI symbol: ha) is an SI accepted metric system unit of area equal to 100 ares (10,000 m2) or 1 square hectometre (hm2) and primarily used in the measurement of land as a metric replacement for the imperial acre.[1] An acre is about 0.405 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 ​1100 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".[1]

Comparison of area units
Unit SI
1 ca 1 m2
1 a 100 m2
1 ha 10,000 m2
100 ha 1,000,000 m2
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
Unit system non-SI metric system
Unit of Area
Symbol ha 
In SI base units: 1 ha = 104 m2


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:[2]

  • The metre for length
  • The are (100 m2) for area [of land]
  • The stère (1 m3) for volume of stacked firewood[3]
  • 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[4] 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"[5]

In 1972, the European Economic Community (EEC) passed directive 71/354/EEC,[6] 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.

Many UK farmers, especially older ones, still use the acre for everyday calculations, and convert to hectares only for official (especially European Union) paperwork. Farm fields can have very long histories which are resistant to change, with names such as "the six acre field" stretching back hundreds of years and across generations of family farmers. Some younger agricultural workers are now beginning to think in hectares as their "first language", though this is more typical of professional consultants and managers than of traditional farming and land-owning families, and in some circles may be viewed as a social class indicator.


Hectare Diagram
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.


The centiare is one square metre.


The deciare is ten square metres.


The are (/ɑːr/[7] or /ɛər/[8]) 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 the modern International System of Units (SI).[9] It is still commonly used in colloquial speech to measure real estate, in particular in Indonesia, India, and in various European countries.

In Russian and other languages of the former Soviet Union, the are is called sotka (Russian: сотка: 'a hundred', i.e. 100 m2). 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.

Etymologically, the word are finds its roots in the Talmudic Aramaic word ארעא (araa), meaning "land".


The decare (/ˈdɛkɑːr, -ɛər/) is derived from deca and are, and is equal to 10 ares or 1000 square metres. It is used in Norway[10] and in the former Ottoman areas of the Middle East and the Balkans (Bulgaria)[11] 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[12]
  • Dunam, dunum, donum, or dönüm in Israel, Palestine, Jordan, Lebanon, Syria and Turkey[13]
  • Mål is sometimes used for decare in Norway, from the old measure of about the same area.


Trafalgar Square, London 2 - Jun 2009
Trafalgar Square has an area of about one hectare.[14]

The hectare (/ˈhɛktɛər, -tɑːr/[15]), although not a unit of SI, is the only named unit of area that is accepted for use within the SI.[16] 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.[17] The United Kingdom,[18] United States, Burma,[19][20] and to some extent Canada use the acre instead.

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".[21]

In many countries, metrication 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:[22]


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[26] 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[1] 100 a 10,000 m2 0.01 km2 2.471 acres[27]
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

International rugby pitch

Hamilton 03
Waikato Stadium – Hamilton, New Zealand
The maximum playing area of an international-sized rugby union pitch is about one hectare

Statue of Liberty

The Statue of Liberty occupies a square of land with an area of one hectare

Interior of all-weather athletics track

Hansen Field
Hansen Field at Western Illinois University in Macomb, Illinois incorporates an all-weather running track
Piste athl%C3%A9tisme-en
The grass in the centre of a standard athletic track is a little over one hectare in extent

See also


  1. ^ This is a standard high school problem in geometry


  1. ^ a b c BIPM (2014). "SI Brochure, Table 6". Retrieved 17 November 2014.
  2. ^ "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-metre square"] (in French). Le CIV (Centre d'Instruction de Vilgénis) – Forum des Anciens. Retrieved 2 March 2010.
  3. ^ Thierry Thomasset. "Le stère" (PDF). Tout sur les unités de mesure [All the units of measure] (in French). Université de Technologie de Compiègne. Retrieved 21 March 2011.
  4. ^ F J Smith. "Standard Kilogram Weights – A Story of Precision Fabrication" (PDF). Platinum Metals Rev., 1973, 17, (2). Retrieved 5 March 2010.
  5. ^ "SI brochure (Chapter 4; Table 6)". International Bureau of Weights and Measures. 2006. Archived from the original on 1 October 2009. Retrieved 5 March 2010.
  6. ^ "Council Directive of 18 October 1971 on the approximation of laws of the member states relating to units of measurement, (71/354/EEC)". Retrieved 7 February 2009.
  7. ^ "are". Oxford Dictionaries. Retrieved 24 December 2010.
  8. ^ "are – definition. American English definition of are by Macmillan Dictionary". Macmillandictionary.com. Retrieved 20 May 2012.
  9. ^ "SI brochure (8th edition)". BIPM. March 2006.
  10. ^ "Decrease in total grain yield". Grain and oil seeds, area and production, 2002. Statistics Norway. Retrieved 16 November 2010.
  11. ^ "Market of agricultural land in Bulgaria". BNR Radio Bulgaria. 5 October 2010. Archived from the original on 22 October 2010. Retrieved 16 November 2010.
  12. ^ Λεξικό της κοινής Νεοελληνικής (Dictionary of Modern Greek), Ινστιτούτο Νεοελληνικών Σπουδών, Θεσσαλονίκη, 1998. ISBN 960-231-085-5
  13. ^ 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 5 May 2009.
  14. ^ "DEPARTMENT FOR ENVIRONMENT, FOOD AND RURAL AFFAIRS, AND RURAL PAYMENTS AGENCY; The Delays in Administering the 2005 Single Payment Scheme in England" (PDF). National Audit Office. 18 October 2006. p. 27.
  15. ^ "hectare". Oxford Dictionaries. Retrieved 24 December 2010.
  16. ^ Bureau international des poids et mesures (2006). "The International System of Units (SI)" (PDF). 8th ed. Retrieved 13 February 2008. Chapter 5.
  17. ^ The Council of the European Communities (27 May 2009). "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 29 January 2010.
  18. ^ "Weights and Measures Act 1985" (PDF). British Government. 1985. Retrieved 17 December 2016.
  19. ^ "Appendix G – Weights and Measures". The World Factbook. CIA. 2006. Retrieved 8 August 2006.
  20. ^ MYA/01/008 Agriculture Sectore Review, Working Paper No. 6 – Agroindustry in Myanmar Archived 15 May 2013 at the Wayback Machine.
  21. ^ "Instructions for the Conversions of Areas to Metric". Law Society of South Africa. November 2007. Retrieved 21 January 2011.
  22. ^ Britannica, unit of measurement, accessed 30 October 2009
  23. ^ 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.
  24. ^ Oscar van Vlijmen (11 September 2006). "Oppervlakte" [Area]. Eenheden, constanten en conversies [Units, constants and conversion] (in Dutch). Retrieved 15 January 2011.
  25. ^ 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.
  26. ^ BS350:Part 1:1974 Conversion factors and tables Part 1. Basis of tables. Conversion factors. British Standards Institution. 1974. p. 7.
  27. ^ 2.4710439 U.S. survey acres or 2.4710538 international acres
  28. ^ "Chinese Measurements – Units of Area". On-line Chinese Tools. Retrieved 24 December 2010.
  29. ^ 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.
  30. ^ "Thailand Property Conversion". Siam Legal (Thailand) Co., Ltd. Retrieved 24 December 2010.
  31. ^ "Law 1 – The Ground". Laws of the Game – Rugby Union 2010. International Rugby Board (IRB). Retrieved 19 December 2010.
  32. ^ "IAAF 400 Metre Standard Track Marking Plan". IAAF. 2008. p. 35. Retrieved 11 February 2013.

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