The hectare is built on a unit most people have never heard of
The hectare, used worldwide for fields, forests and building plots, is really a hundred of something else. That something is the are, a ten-by-ten-metre square introduced by revolutionary France. The are was left out when the metric system was modernised in 1960, yet its hundredfold offspring became the default way to measure land.
A hectare is a square 100 metres on each side, or 10,000 square metres. A hundred of them make a square kilometre, and one hectare is about 2.47 acres. The name joins the prefix hecto, meaning a hundred, to are, which the French coined from the Latin word for an open area. The law that first gave the metric system legal standing, passed on 7 April 1795, defined the are alongside a handful of other units, among them the stère, a cubic metre used for stacked firewood.
Other prefixes spawned relatives. The decare, ten ares, survives in Norway and in lands once ruled by the Ottomans, where traditional measures called the dunam or dönüm were redefined to match it. In Russian, an are is a sotka, meaning a hundred, and many suburban dachas are described as six sotki. Mexico writes land areas as hyphenated combinations of hectares, ares and centiares. Across Indonesia, India and parts of Europe, people still speak of ares when discussing property, and older units in several countries, including China's gongqing, were redefined as exactly one hectare.
Officially, the hectare's status has slipped. After 1960 it was classed as a non-SI unit accepted for use alongside the system, and a 1972 European directive allowed the are, and so the hectare, strictly for land. By 2026, the international measurement bureau in France had stopped listing it as accepted at all.
In practice, none of that has dented its popularity. It is the legal unit for land deeds, farming, forestry and planning across the European Union, the United Kingdom, Canada, Australia, New Zealand and South Africa. The United States and Myanmar are the holdouts that still measure land in acres.
Source: Hectare
