What an acre and a hectare actually measure
An acre and a hectare both measure land area, and the only thing that separates them is which civilisation defined them. The acre is a survivor of medieval English field practice: a strip one chain wide by one furlong long, which is 66 feet by 660 feet, or 43,560 square feet. That shape was roughly what one man with one ox team could plough in a day, so the acre began as a measure of labour and only later hardened into a measure of area. The hectare came out of the metric reform and carries no history at all: it is a square 100 m on a side, exactly 10,000 square meters.
Because the acre is now defined through the foot, and the foot has been defined in meters since 1959, every factor on this page is exact rather than measured. The International Yard and Pound Agreement fixed the yard at 0.9144 m, which makes the foot 0.3048 m and the square foot 0.09290304 m². Multiply that by 43,560 and you get 4,046.8564224 m² per acre, with no rounding anywhere in the chain. Divide 10,000 by that and one hectare is 2.4710538147 acres.
You need this conversion whenever a document crosses a border or a discipline. A US deed states acres, a European land registry states hectares, a builder's takeoff wants square feet, an agronomist's spray rate is per hectare, and a mapping package outputs square meters. Getting the parcel into one common unit first — this calculator uses square meters as the pivot — is what keeps a fertiliser rate or a purchase price from being wrong by a factor of 2.47.
The conversion factors and where each one comes from
Every conversion here is a single multiplication, so the only thing that can go wrong is the number you multiply by. Each of those numbers is derived, not looked up:
- Square foot to square meter: 0.09290304. This is 0.3048². Because the foot is defined as exactly 0.3048 m, the square foot is exact too.
- Acre to square foot: 43,560. A chain is 66 ft and a furlong is 660 ft, and 66 × 660 = 43,560. Equivalently, 10 square chains.
- Acre to square meter: 4,046.8564224. That is 43,560 × 0.09290304, carried out in full.
- Hectare to square meter: 10,000. A definition, not a derivation.
- Acre to hectare: 0.40468564224. That is 4,046.8564224 ÷ 10,000, so the digits are simply the previous factor shifted four places.
- Square mile to acre: 640. A mile is 80 chains, so a square mile is 6,400 square chains, and an acre is 10 square chains.
The calculator converts your entry to square meters first and then out to each target unit. That is deliberate: with a pivot unit there are only seven factors to be right about instead of forty-two, and a mistake in one of them shows up in every output at once rather than hiding in a single unusual pair.
The rectangular-lot mode adds one step in front. It multiplies length by width in feet to get square feet, then applies the same chain. If your lot is not a rectangle, do not force it into this mode — use the field acreage calculator, which handles irregular boundaries.
Worked example: a 150 ft by 200 ft building lot
You are looking at a suburban lot measured at 150 feet along the road and 200 feet deep, and the county wants the area in acres while the architect wants square meters.
- Area in square feet. 150 × 200 = 30,000 ft².
- Area in square meters. 30,000 × 0.09290304 = 2,787.0912 m².
- Area in acres. 30,000 ÷ 43,560 = 0.688705 acre. Check it by the metric route: 2,787.0912 ÷ 4,046.8564224 = 0.688705, the same figure.
- Area in hectares. 2,787.0912 ÷ 10,000 = 0.27870912 ha.
- Sanity check against the acre's shape. An acre is 43,560 ft² and this lot is 30,000 ft², so it should come out at 30,000/43,560 = 68.87% of an acre. It does.
A useful second reference point: a US football field including both end zones is 360 ft by 160 ft, which is 57,600 ft², or 57,600 ÷ 43,560 = 1.3223 acres. So this lot is a little over half a football field.
How to read the result
Read the unit your audience uses, and keep the others for cross-checking. Three anchors make the numbers feel real. A quarter-acre — 10,890 ft², or one rood in the old English system — is the classic North American suburban lot. A hectare, at 2.47 acres, is about two and a half of those. A square mile, at 640 acres or 259 hectares, is one section of the US Public Land Survey System and is the unit farm and ranch acreage is usually quoted against.
Precision deserves a thought too. A deed quoting "5.00 acres" is claiming a hundredth of an acre, which is 435.6 ft² — larger than many garden sheds. Quoting your converted answer to six decimal places implies a survey accuracy nobody has. Round to the precision of your input: a parcel described as "about 5 acres" converts to "about 2 hectares", not to 2.023428 hectares.
Watch the difference between gross and net acreage. Gross acreage is everything inside the boundary; net acreage subtracts road easements, utility rights of way, wetlands and setbacks. The conversion arithmetic is identical either way, but the two figures can differ substantially on a parcel fronting a highway, and only the deed or plat tells you which one you are holding.
Exact land-area conversion reference
| One unit of | Square meters | Square feet | Acres | Hectares |
|---|---|---|---|---|
| Square foot | 0.09290304 | 1 | 0.000022957 | 0.0000092903 |
| Square meter | 1 | 10.7639104 | 0.000247105 | 0.0001 |
| Square yard | 0.83612736 | 9 | 0.000206612 | 0.0000836127 |
| Square rod | 25.29285264 | 272.25 | 0.00625 | 0.0025292853 |
| Rood (quarter-acre) | 1011.7141056 | 10,890 | 0.25 | 0.1011714106 |
| Acre | 4046.8564224 | 43,560 | 1 | 0.4046856422 |
| Hectare | 10,000 | 107,639.104 | 2.4710538147 | 1 |
| Square kilometer | 1,000,000 | 10,763,910.4 | 247.105381 | 100 |
| Square mile | 2,589,988.110336 | 27,878,400 | 640 | 258.9988110336 |
The square rod is 16.5 ft on a side and 160 of them make an acre, which is why old deeds describe parcels in rods and perches.
Mistakes that corrupt a land-area conversion
- Using the US survey acre without meaning to. Before 2023 the US survey foot (1200/3937 m) coexisted with the international foot, making the survey acre 4,046.87261 m² — about 4 parts per million larger. NIST and NOAA retired the survey foot at the end of 2022 for new work, but older state-plane survey data still carries it. On a single house lot the difference is invisible; across a township it is metres of position.
- Multiplying instead of dividing. Acres to hectares is a multiplication by 0.4047; hectares to acres is a multiplication by 2.471. Getting them backwards is an error of a factor of 6.1, and the result is usually still a plausible-looking number.
- Squaring a linear factor once instead of twice. A meter is 3.28 feet, so a square meter is 3.28² = 10.76 square feet. Applying 3.28 to an area understates it by a factor of 3.28.
- Forcing an irregular parcel through the rectangle mode. Length × width is only the area of a rectangle. A pie-shaped cul-de-sac lot or a river-bounded field needs a coordinate or triangle method.
- Confusing the deed area with the surveyed area. Deeds are frequently copied forward for a century. Where a plat and a modern survey disagree, the survey and the physical monuments govern, not the arithmetic.
- Reporting more digits than the measurement supports. A tape measurement good to a foot on a 150 ft frontage is a 0.7% uncertainty, which is about 0.005 acre on the worked example — already bigger than the third decimal place.
Where this sits among the other area tools
This calculator handles the pure unit conversion, which is the part that has one right answer. The harder question is usually where the area came from. For a plain building-footprint or floor-plan conversion, the square feet to square meters calculator is the more direct tool because it skips the land units entirely. For a field with an irregular boundary, measure it as a set of triangles or GPS points with the field acreage calculator, then bring the answer here to restate it.
Once you have the area right, most downstream decisions are rate calculations against it. Seed and fertiliser rates are quoted per acre in the US and per hectare almost everywhere else, which is exactly the conversion this page exists for — see the lawn fertilizer rate calculator and the plant population per acre calculator. For bulk materials spread over an area, thickness turns area into volume, and the cubic yards to cubic feet calculator takes it from there.
One last convention worth knowing: land in parts of Asia and in older European records uses units this calculator does not carry — the are (100 m², one hundredth of a hectare), the Indian bigha, which has no single national value, and the Japanese tsubo of about 3.306 m². Where a local unit has no fixed legal definition, convert to square meters using the value the local registry publishes rather than any single figure quoted online.