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Comparison of Area units
Unit SI SI base
1 ca 1 m2 1 m2
1 a 1 dam2 102 m2
1 ha 1 hm2 104 m2
100 ha 1 km2 106 m2
non-SI comparisons
non-SI metric SI base
0.00386102 sq mi 1 ha 104 m2
2.471 acre 1 ha 104 m2
107,639 sq ft 1 ha 104 m2

A hectare (symbol ha, pronounced /ˈhɛktɛər/) is a unit of area equal to 10,000 square metres (107,639 sq ft), or one square hectometre (100 metres, squared), and is commonly used for measuring land area.

Its base unit, the are, was defined by older forms of the metric system, but is no longer part of the modern metric system known as the International System of Units (SI). The International Committee for Weights and Measures (CIPM) classifies the hectare as a unit that is accepted for use with SI.[1]



The metric system of measure was first put onto 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 stere (1 m3) for volume of 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 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 had not received international recognition. The CGPM made no mention of the are in its publication, but gave the hectare a qualified recognition. In 2006 the hectare was recognised as a "Non-SI units 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 implicity the hectare) whose use was limited to the measurement of land.

Land Measurement

Trafalgar Square which has an area of about one hectare.[6]

The hectare is widely used throughout the world[1] and is the legal unit of measure in domains concerned with land ownership, land planning, and management, including law (land deeds), agriculture, forestry, and town planning throughout the European Union[7], though the United States, Myanmar, and to some extent Canada instead use the Imperial measurement unit of area - the acre (0.404686 ha). Some of the former Ottoman countries and Norway and Botswana use the decare, one tenth of a hectare.[citation needed].

Even in countries that have undergone a general conversion from traditional English measurements to metric measurements (e.g. Canada), legal descriptions relating to land, which frequently use the acre, have not been converted, as doing so would require a resurvey of the land.[citation needed]

In many counties the advent of metrication has meant that national units of measure were either redefined or clarified in terms of metric unit. The following legacy units of area has been redefined as being equal to one hectare:[8]


Metric and Imperial Comparisons
Units Symbol Metric Equivalents Imperial Equivalents
centiare ca 1 m2 0.01 a 1.19599 yd2
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 2.47105 acres
square kilometre km2 100 ha 1,000,000 m2 0.38610 miles2

The most commonly used units are in bold.

One hectare is also equivalent to:

See also


  1. ^ a b Bureau International des Poids et Mesures (2006). The International System of Units (SI). 8th ed.. Retrieved 2008-02-13.  Chapter 5.
  2. ^ "La loi du 18 Germinal an 3 (The law of 18 Germanial year 3) « la mesure [républicaine de superficie pour les terrains, égale à un carré de dix mètres de côté »"]. Le CIV (Centre d'Instruction de Vilgénis) - Forum des Anciens. Retrieved 2010-03-02. 
  3. ^ F J Smith. "Standard Kilogram Weights - A Story of Precision Fabrication". Retrieved 2010-03-05. 
  4. ^ "SI brochure (Chapter 4)". International Bureau of Weights and Measures. 2006. Retrieved 2010-03-05. 
  5. ^ "Council Directive of 18 October 1971 on the approximation of laws of the member states relating to units of measurement, (71/354/EEC)".,nl&lng2=da,de,el,en,es,fr,it,nl,pt,&val=22924:cs&page=1&hwords=. Retrieved 2009-02-07. 
  6. ^ [ "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. Retrieved 2010-02-24. 
  7. ^ 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. 
  8. ^ Britannica, unit of measurement, accessed 2009-10-30

External links


Simple English

One Hectare is a unit of measurement. It measures the area of something. It is equal to 2.47 acres. A hectare is 10,000 square meters.

A square plot of land with 100 m length for a side, is one hectare.


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