Acres to Hectares Converter

acres to hectares — quick reference

The formula, worked line by line

An acre is defined as 4,840 square yards, and the international yard has been exactly 0.9144 m since 1959. That makes an acre exactly 4,840 times 0.9144 squared, which is 4,046.8564224 m². A hectare is exactly 10,000 m² by definition, being the area of a 100 m square. The ratio between them is therefore an exact rational number, not a measured one.

Written out, the factor is 0.40468564224, and it terminates. Every rounded version you see in print — 0.4047, 0.405, or the two-and-a-half-acres rule of thumb — is a convenience, not a competing definition, so a tool and a textbook should never disagree on the underlying number.

hectares = acres × 0.40468564224
         = acres × 4,046.8564224 m² ÷ 10,000 m²
acres = hectares ÷ 0.40468564224 = hectares × 2.4710538…
160 acres → 160 × 0.40468564224 = 64.7497 ha

The multiply-by-0.4 shortcut reads 1.16 percent low, and unlike a speed conversion the error here scales with something valuable. On 10 acres it loses 0.05 ha, which is nothing. On 1,000 acres it loses 4.7 ha, close to twelve acres of land quietly disappearing, and on a per-hectare yield or subsidy figure that 1.16 percent propagates straight into the money.

Use the shortcut to picture a parcel and the exact factor whenever the number is attached to a contract, a claim, or a comparison between two properties.

One historical wrinkle, and it matters more for area than for length. US land surveys long used the slightly longer US survey foot, defined as 1200/3937 m, which is about two parts per million above the international foot. Squared for area that becomes roughly four parts per million, making a survey acre about 4,046.873 m² against the international 4,046.856 — larger by some 0.016 m², or about 25 square inches per acre.

NIST and the National Geodetic Survey deprecated the US survey foot on 31 December 2022, and from 1 January 2023 the international foot is the single US definition. This converter uses it.

How to use the acres to hectares converter

Acres are how US land is deeded, listed, and talked about. Hectares are how almost everyone else measures it: agricultural statistics, conservation reporting, research papers, subsidy applications, and any buyer or partner outside North America. When your parcel has to be understood abroad, enter the acreage here and read off the hectares; Swap converts a metric figure back.

The factor behind the conversion is exact rather than approximate, because an acre is defined as 4,840 square yards and the international yard has been exactly 0.9144 metres since 1959, which pins the acre at exactly 4,046.8564224 m². A hectare is exactly 10,000 m², so the ratio between them carries no measurement uncertainty at all.

The scale is easy once you have a few pegs, and the US survey grid supplies the bigger ones, which are worth memorising because so much American land is described by them. The full 640-acre section is one square mile of the Public Land Survey System.

For rough conversion, multiply acres by 0.4, or just divide by 2.5. It runs about 1.16 percent low: 100 acres gives 40 ha against a true 40.47, and 250 acres gives 100 ha against 101.17.

That is close enough for conversation and well inside how precisely most parcels are described in casual use, but not close enough for a deed, a subsidy claim, or a per-hectare yield figure, where a 1 percent slip on a large holding is real land and real money.

Why is an acre such an odd number?

The two units come from completely different mental pictures, which is why neither converts intuitively into the other. An acre is a medieval work unit: one chain by one furlong, 66 ft by 660 ft, a long thin strip that an ox team could plough in a day, which fixes it at 43,560 square feet.

A hectare is pure decimal geometry, a 100 m by 100 m square of 10,000 m², with 100 hectares making exactly one square kilometre. For physical reference points, an American football field including both end zones is 1.32 acres or 0.5351 ha, and a football pitch at 105 m by 68 m is 1.7644 acres or 0.7140 ha.

Every acres value, worked out

52 common acres figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask