The hectare is a metric unit of area defined as 10,000 square metres, and primarily used
in the measurement of land. In 1795, when the metric system was introduced, the "are"
was defined as 100 square metres and the hectare was thus 100 "ares" or 1⁄100 km2. An acre
is about 0.4047 hectare and one hectare contains about 2.47 acres.
When the metric system was further rationalised in 1960, resulting in the International System
of Units, 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 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
defined five units of measure: The metre for length
The are 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 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. 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, the are did not receive international recognition.
The International Committee for Weights and Measures makes no mention of the are in the
current 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 passed
directive 71EEC, 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 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. Centiare
The centiare is a synonym for one square metre. Deciare
The deciare is ten square meters Are
The are is a unit of area, equal to 100 square metres, used for measuring land area. It was
defined by older forms of the metric system, but is now outside of the modern International
System. It is commonly used to measure real estate,
in particular in Indonesia and in French-, Portuguese-, Slovakian-, Czech-, Polish-,
Dutch-, and German-speaking countries as also in India.
In Russia and other former Soviet Union states, the "sotka" 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 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 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.
Hectare The hectare, 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, 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
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. The following legacy units of area have been redefined as being equal to one
hectare: Jerib in Iran
Djerib in Turkey Gong Qing in mainland China
Manzana in Argentina Bunder in The Netherlands
Conversions The most commonly used units are in bold.
One hectare is also equivalent to: 15 mǔ or 0.15 qǐng
10 dunam or dönüm 10 stremmata
6.25 rai ≈ 1.008 chō
≈ 2.381 feddan Visualising a hectare
Visitors to London can visualize a hectare by visiting Trafalgar Square.
International rugby field Statue of Liberty
Interior of all-weather athletics track See also
Conversion of units Hecto-
Hectometre Order of magnitude
Notes and references
External links Official SI website: Table 6. Non-SI units
accepted for use with the International System of Units