A hectare is 10,000 square metres, a square 100 metres on a side. It equals 2.471 acres and is the working unit of land measurement in most of the world outside the United States.

The word was coined in 1795 during the French Revolution, when the new republic was rebuilding its weights and measures from scratch. It combines the Greek hekaton, meaning hundred, with the older unit are. A hectare is roughly the size of a rugby pitch, or two and a half American football fields.

Where you meet it

• Farm size and land registries in most countries
• Crop yields expressed as tonnes per hectare
• Forestry and conservation planning
• Agricultural subsidies and environmental reporting

American farmers still think in acres, and that difference trips people up in international trade and research. A 100-hectare farm is about 247 acres. A yield of 10 tonnes per hectare is roughly 150 bushels per acre for maize, which is a good crop in most regions.