Area Converter
Square metres, square feet, acres, hectares and square miles, on the exact defined factors. Every answer also comes with the side of the equivalent square, because an area is a quantity and not a shape.
Convert an area
The measurement you have, in the unit chosen below.
The unit the measurement is already in.
The unit you want the answer in. Every other unit is listed underneath the result anyway.
Everything routes through the square metre: 1 ac is 4,046.856422 m², and one ft² is exactly 0.09290304 m².
- Conversion factor
- 1 ac = 43,560 ft²
- Reverse factor
- 1 ft² = 0.00002295684114 ac
- In square metres
- 4,046.856422 m²
- As a square
- 63.61490723 m on each side — an area is not a shape, and this is the one shape a single number can describe
- Hectares and acres
- 0.4046856422 ha = 1 ac
- Definition
- One square foot is exactly 144 square inches, or 0.09290304 m² — the square of the exactly 0.3048 m foot.
| Unit | Symbol | Value |
|---|---|---|
| Square millimetres | mm² | 4,046,856,422 |
| Square centimetres | cm² | 40,468,564.22 |
| Square metres | m² | 4,046.856422 |
| Hectares | ha | 0.4046856422 |
| Square kilometres | km² | 0.004046856422 |
| Square inches | in² | 6,272,640 |
| Square feet | ft² | 43,560 |
| Square yards | yd² | 4,840 |
| Acres | ac | 1 |
| Square miles | mi² | 0.0015625 |
Every conversion goes through the square metre
Ten units could be connected by 100 direct factors, and a table that size cannot be kept consistent. Instead each unit is stored as one number — how many square metres it is — and every conversion is two steps.
m² = value × f(from) • result = m² ÷ f(to)- f(u)
- Square metres in one unit u — 4,046.8564224 for the acre
- m²
- The measurement in the SI unit of area
- result
- The measurement in the unit you asked for
Area factors are the square of length factors
Every number in the table above is a length factor multiplied by itself. A foot is exactly 0.3048 m, so a square foot is exactly 0.3048² = 0.09290304 m². An inch is exactly 0.0254 m, so a square inch is exactly 0.00064516 m². Nothing here is measured; it is all the 1959 international yard and pound agreement, squared.
Squaring the factor also squares its error, and that is the practical reason to carry exact values rather than convenient ones. A length conversion that is 1% wrong gives an area about 2% wrong, because 1.01² is 1.0201. Rounding 3.280839895 ft/m down to a memorable “3.28” is a slip of 0.026% in a length and 0.051% in an area — five square metres on a one-hectare site, from a shortcut that looked harmless.
An acre is an area, not a shape
The acre is 43,560 ft², and the number is inherited rather than designed. An acre was one furlong by one chain — 660 feet by 66 feet — the strip a team of oxen could plough in a day. It was long and thin because turning the plough was the expensive part of the day. Multiply 660 by 66 and the awkward 43,560 falls out, and it has outlived the oxen, the furlong and the chain.
The hectare is the deliberately tidy answer to all of that: a square exactly 100 m on a side, 10,000 m², about 2.471 acres. Because “how big is an acre” is asked far more often than “how many square feet is an acre”, the result panel reports the side of the equivalent square alongside the conversion — one acre is a square 63.61 m, or 208.71 ft, on a side. That square is one shape among infinitely many with the same area, which is exactly the point.
Results are rounded to twelve significant figures rather than to a fixed number of decimal places. This tool spans the square millimetre to the square mile — twelve orders of magnitude — and no single decimal place is readable at both ends. Significant figures are also what makes one acre come back as exactly 43,560 ft²: 4046.8564224 ÷ 0.09290304 in binary floating point is 43559.99999999999.
A 0.34-acre building lot
Step one: 0.34 × 4,046.8564224 = 1,375.93 square metres. Step two, into square feet: 1,375.931184 ÷ 0.09290304 = 14,810.4 ft². And in the unit a European agent would use, 0.34 × 0.4046856422 = 0.1375931184 hectares. All three describe the same piece of ground.
To picture it, take the square root of the square metres: √1,375.931184 = 37.09 m, so the lot is the size of a square about 37 metres — 122 feet — on a side. It almost certainly is not that shape; that is the number for judging whether it is big.
Now the squaring trap, with real numbers. A lot measured at 100 by 150 feet is 15,000 ft². Converted with the exact factor, 15,000 × 0.09290304 = 1,393.5456 m². Converted with a rounded 0.305 m/ft instead — a length factor only 0.066% too large — you get 0.305² = 0.093025 and therefore 1,395.375 m². The answer is 1.83 m² too big. The length shortcut was off by two parts in three thousand and the area came out off by four, which is the whole reason this page carries defined values to twelve figures instead of the friendly ones.
What this converter assumes
- The foot, yard, inch, mile and acre are the international ones defined in 1959. The US survey acre, about 4 parts per million larger, is deliberately not offered — the survey foot it is built on was retired for new work at the end of 2022.
- The “as a square” figure is one shape among infinitely many enclosing that area. It is there to make a number picturable, not to imply dimensions.
- Areas here are planar. A sloped roof or a hillside has more surface than its footprint on a map, and no unit conversion can recover the difference — that needs the pitch as well.
- An area is a magnitude, so negative values are rejected. If you are converting a difference between two measurements, convert its size and keep the sign yourself.
- Results carry twelve significant figures internally and are displayed to ten. Neither is a claim about your measurement — a site paced out to the nearest metre is still only good to the nearest metre after conversion.
- Nothing here converts between area and length or volume. Those scale as the first and third powers of a length factor, which are different calculations and different tools.
Area conversion FAQ
How many square feet are in an acre?
Exactly 43,560. The number looks arbitrary because it is inherited rather than designed: an acre was one furlong long by one chain wide — 660 feet by 66 feet — the strip of land a team of oxen could plough in a day. Long and thin, because turning the plough was the slow part. Multiply 660 by 66 and you get 43,560, and that product outlived the oxen, the furlong and the chain.
How big is an acre, really?
If you make it a square, it is 208.71 feet — 63.61 metres — on each side. For a rough mental picture, an American football field between the goal lines is 300 by 160 feet, which is 48,000 ft², so an acre is a little under one of those. But an acre has no shape at all: a square, the original 660 × 66 strip, and a long ribbon along a river can all be exactly one acre. That is why this converter reports the side of the equivalent square rather than pretending an area implies dimensions.
How many acres are in a hectare?
2.471053815 acres. Going the other way, one acre is 0.4046856422 hectares. A hectare is exactly 100 metres by 100 metres — 10,000 m² — which is the point of it: it is the deliberately tidy metric answer to a unit that was never tidy. Land is quoted in hectares almost everywhere except the United States and, for farmland and property, the United Kingdom and Ireland.
Why isn't a square foot about a third of a square metre?
Because area squares the ratio. A foot is 0.3048 of a metre, roughly a third, so it is tempting to expect a square foot to be about a third of a square metre. It is not: 0.3048² = 0.09290304, so a square foot is about a *ninth* of a square metre, and one square metre is 10.76391042 square feet. The same trap catches yards — a square yard is 9 square feet, not 3.
Why does a small rounding error matter more for area than for length?
Because squaring a factor also squares its relative error. Take a lot measured at 100 by 150 feet, 15,000 ft². Convert with the exact 0.3048 m/ft and you get 1,393.5456 m². Convert with a rounded 0.305 m/ft — only 0.066% high — and you get 1,395.375 m², which is 1.83 m² too much. The length factor was off by two parts in three thousand; the area came out off by four. As a rule of thumb, an x% error in a length conversion becomes about 2x% in an area, and about 3x% in a volume.
How many acres are in a square mile?
Exactly 640. That is not a coincidence of rounding — it is how the square mile is defined in the US Public Land Survey System, where one square mile is a 'section' and 36 sections make a township. Quarter sections of 160 acres are the units the 1862 Homestead Act was written in, which is why so much of the American Midwest is still laid out on a 160-acre grid you can see from a plane.
What is the US survey acre, and do I need it?
Almost certainly not. Before 1959 the United States used a slightly different foot, defined as 1200/3937 metres, about 2 parts per million longer than the international foot. Squaring it makes the survey acre about 4 ppm larger than the international acre — roughly 10 m² across a whole 640-acre section. NIST and the National Geodetic Survey retired the survey foot for new work on 31 December 2022, so this converter offers only the international acre. If you are reconciling pre-2023 state plane coordinates or an old deed, that is the one case where the difference is real.
Is the hectare an SI unit?
No. The SI unit of area is the square metre; the hectare is a non-SI unit that the General Conference on Weights and Measures accepts for use alongside the SI, specifically for expressing land area. Its sibling the 'are' — 100 m², the unit the hectare is a hundred of — is essentially extinct outside a few European land registries.
Sources and review notes
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), including the exact conversion factors used here
- NIST — U.S. Survey Foot: revised unit conversion factors, and the 31 December 2022 deprecation that also retires the survey acre
- BIPM — The International System of Units (SI) Brochure, for the square metre and the status of the hectare
The factors on this page are defined values rather than measured ones, so they do not go stale: the acre has been 43,560 square feet for centuries and exactly 4,046.8564224 m² since the foot was fixed in 1959, and the hectare has been exactly 10,000 m² since it was invented. The only recent change is the retirement of the US survey foot, and with it the survey acre, which this tool never offered.