Acres to Hectares

The acre and the hectare are the two units that divide the world's land records: acres in the United States, the United Kingdom, Ireland and across the Commonwealth; hectares almost everywhere else. Anyone dealing with rural land across that boundary needs the conversion constantly.

One acre is 0.40468564224 hectares. Put the other way, one hectare is 2.4710538 acres, so a hectare is just under two and a half acres. The acre figure is always the smaller number when both describe the same piece of land, which is a useful check when you are reading a document that quotes both.

Where both numbers come from

An acre is defined as 43,560 square feet — historically the area one team of oxen could plough in a day, which is why it is not a round number in any modern system. In metric that is 4,046.8564224 square metres, arrived at by converting 43,560 square feet at exactly 0.09290304 square metres per square foot.

A hectare is exactly 10,000 square metres: a square 100 metres on each side. It was created with the metric system as a land unit, and it divides by ten and a hundred cleanly, which the acre does not. Dividing 4,046.8564224 by 10,000 gives the 0.40468564224 hectares in one acre.

Sizes worth knowing by heart

• 1 acre = 0.4047 ha · 43,560 ft² · 4,840 yd² · 4,046.86 m²
• 10 acres = 4.0469 ha — a smallholding
• 100 acres = 40.469 ha — a working farm
• 640 acres = 258.999 ha — one square mile
• 1 hectare = 2.4711 acres · 10,000 m²
• A square kilometre = 247.105 acres = 100 hectares

The relationship between the square mile and the acre is exact and worth remembering: a square mile is exactly 640 acres. It is the reason the United States' Public Land Survey System divides land into sections of one square mile.

Worked examples

A 12 acre field converts to 4.856 hectares. A 40 acre plot is 16.187 hectares — very close to the 16 hectare figure a European buyer might be quoted, which is the kind of near-match that makes it easy to think two listings are the same when they are not.

Working in the other direction for a sanity check: a 100 hectare farm is 247.105 acres, and a 500 hectare estate is 1,235.53 acres. If those numbers feel uncomfortable, you have probably applied the factor in the wrong direction.

Which unit to put in a contract

Put both. Land contracts that cross a jurisdiction boundary — an overseas buyer, a foreign lender, a multinational developer — should state the area in the unit of the local registry and in the other, with the conversion factor written out. An acre/ha discrepancy of a few hundredths looks trivial on paper but is real money on a large parcel, and a single stated figure in the “wrong” unit invites a dispute later.

For farmland, remember that the area sold and the area cultivated are rarely identical. Hedgerows, ditches, access tracks, woodland strips and building footprints all sit inside the boundary but outside the productive area. Expect the usable area to be several percent smaller than the registered area, and sometimes much more on old irregular parcels.