Area Converter: Square Meters, Hectares and Acres

The area converter changes a value between eleven units of area: square millimeter (mm²), square centimeter (cm²), square meter (m²), square kilometer (km²), hectare (ha), square inch (in²), square foot (ft²), square yard (yd²), acre (ac), square mile (mi²) and the Chinese mu. Type on either side and the opposite field follows; the All Units list shows the same quantity in every unit.

Updated 2026-09-30Reviewed by CalcX Editorial Team5 sources5 min read

What the area converter does

The factors are exact definitions. Every unit reduces to the square meter: a hectare is 10,000 m², the international acre is 4,046.8564224 m² and a square foot is 0.09290304 m². For lengths and volumes, see the length converter and the volume converter; for typed arithmetic, the scientific calculator.

How to use it

Choose the two units.The page opens with square millimeter left and square centimeter right; both dropdowns list all eleven.
Type the value.The other field converts as you type — 1 mm² reads 0.01 cm² — and the All Units list follows.
Use an expression when it helps.10*10+100 shows the hint = 200 and converts as 200 acres, reading 80.937128448 ha; Enter or = settles it.
Swap, or pick from the list.The arrow button exchanges the units and carries the value shown; clicking a list row moves that unit to the active side. The keypad button opens an embedded calculator.

Worked examples

Every readout below comes from this converter.

One acre in the list. 1 ac reads 4,046.8564224 m², 43,560 ft², 4,840 yd², 6,272,640 in², 0.4046856422 ha, 0.0040468564 km² and 0.0015625 mi² — the definitions being 1 acre = 4,840 yd² = 43,560 ft² = 1/640 mi².

Hectares against acres.

Input	Readout
1 hectare	2.4710538147 ac
100 hectares	247.105381467 ac
1 acre	0.4046856422 ha
25 acres	10.117141056 ha
1 mu	666.666666667 m²

The mu is the Chinese land unit, fixed at exactly 2000/3 m².

Square feet against square meters. 1 ft² reads 0.09290304 m² and 1,000 ft² read 92.90304 m²; reversed, 1 m² reads 10.7639104167 ft² and 1,000 m² read 10,763.9104167 ft². The two factors are reciprocals. 1 ft² is also 144 in², and 1 in² reads 6.4516 cm², with the reverse reading 0.15500031 in².

A square mile. 1 mi² reads 640 ac, 2,589,988.1103 km², 2,589,988.11034 m², 27,878,400 ft², 258.998811034 ha and 2,589,988,110,340 mm²; the last readout rounds the defined 2,589,988.110336 m².

Where the factors come from

The square meter is the SI unit of area, and prefixes square with the unit: 1 km² is 10⁶ m², 1 cm² is 10⁻⁴ m² and 1 mm² is 10⁻⁶ m². A hectare is a 100 m × 100 m square, 10,000 m², so 100 hectares make one square kilometer.

The imperial units rest on the 1959 international yard of exactly 0.9144 m: the foot is 0.3048 m, the inch 25.4 mm and the mile 1,609.344 m. Squaring gives in² = 6.4516 cm², ft² = 0.09290304 m², yd² = 0.83612736 m² and mi² = 2,589,988.110336 m². The international acre is 4,840 yd² of that yard, 4,046.8564224 m².

Reading results and limits

Display rule.: Results keep 12 significant digits and at most 10 decimal places, with thousands separators; zero prints as 0. The two rules interact: 1 acre reads 4,046.8564224 m², 1 square mile reads 2,589,988.11034 m², and 1 hectare reads 2.4710538147 ac — the exact 2.471053814671… stops at the ten-decimal cap.
Extremes.: At the extremes the shape changes. At 10¹⁵ and above, and below 10⁻¹⁰, results print exponentially with six decimals: 10⁹ km² reads 1.000000e+15 m²; 1 mm² reads 1.000000e-12 km², and in square miles 3.861022e-13 mi². The threshold is strict and the stored value decides a border case: 1 mm² in hectares reads 1.000000e-10 ha, while 1 cm² in square kilometers reads 0.0000000001 km².
Ten-decimal cap at the small end.: The ten-decimal cap swallows digits at the small end: 1 mm² in acres reads 0.0000000002 ac, while the square-meter row keeps 0.000001 m². Swap carries the displayed value, so a round trip can return rounded text: 1,000 m² → ft² reads 10,763.9104167, and swapping back reads 999.999999999 m²; 1 km² → mi² reads 0.3861021585 and swaps back as 0.9999999999 km².
Area only.: It does not convert length or volume: distances and dimensions live on the length converter and liquid or solid volumes on the volume converter.

Common mistakes

Factor direction. 1,000 ft² is 92.90304 m², not 10,763.9104167 m²; the larger number is what 1,000 m² reads in square feet.
Acre and hectare rounded twice. 25 acres is 10.117141056 ha and 1 ha is 2.4710538147 acres; repeating the "0.4" or "2.47" shortcut compounds the error.
Typing a rounded readout back in. 1 acre in hectares reads 0.4046856422; enter that on the hectare side and square meters read 4,046.856422 — four ten-millionths below the defined acre. For a contract, use 1 acre = 4,840 yd².
International versus U.S. survey acre. Documents drawn up before 2023 may use the survey acre, about four parts per million larger; NIST retired the survey foot at the end of 2022, and this list carries only the international acre.

Where it is used

Land and property listings. Acres and hectares for plots and fields: 1 acre is 0.4046856422 ha, and 25 acres is 10.117141056 ha.
Floor plans and interiors. Square feet to square metres for rooms and materials: 1,000 ft² is 92.90304 m², and 1 m² is 10.7639104167 ft².
Farmland measures in China. The mu, fixed at exactly 2000/3 m², converts beside the hectare for land documents.

Sources

BIPM, The International System of Units (SI Brochure), 9th edition — the metre and the derived square metre, plus the SI prefixes behind mm², cm² and km². bipm.org （访问日期：2026-09-30）
NIST, Special Publication 811, Appendix B.8 — hectare (10 000 m², exact), square inch (6.4516 × 10⁻⁴ m²), square foot (9.290 304 × 10⁻² m²) and square yard factors. nist.gov （访问日期：2026-09-30）
NIST, Handbook 44 (2026), Appendix C — the international acre as 43 560 square feet exactly and 4 046.856 422 4 m². nist.gov （访问日期：2026-09-30）
Wikipedia, Acre — 4 840 square yards, the 1959 international yard and the survey acre's four-parts-per-million difference. en.wikipedia.org （访问日期：2026-09-30）
Wikipedia, Hectare — 10 000 m², the 100 m square and 100 hectares per square kilometre. en.wikipedia.org （访问日期：2026-09-30）