Area Converter
Square meters through square miles in one tool, including the are, which European land listings use and most English-language converters leave out.
Most used area tools
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Every factor here is exact, not rounded. A hectare is exactly 10,000 square meters and an acre is exactly 4,046.8564224 square meters, because the foot has been exactly 0.3048 meters since 1959. The 2.47 you see quoted for hectares to acres is a rounding of 2.4710538.
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Reference table
| Unit | Square meters | Status |
|---|---|---|
| 1 m² | 1 | exact |
| 1 km² | 1000000 | exact |
| 1 ha | 10000 | exact |
| 1 a | 100 | exact |
| 1 ac | 4046.8564224 | exact |
| 1 ft² | 0.09290304 | exact |
| 1 yd² | 0.83612736 | exact |
| 1 in² | 0.00064516 | exact |
| 1 mi² | 2589988.110336 | exact |
Every value above is exact. The metric units are exact by definition, and the imperial and US customary units are exact because the yard has been exactly 0.9144 meters since the 1959 international agreement.
The are, and reading an Italian land record
An are is 100 square meters. A hectare is 100 ares. A centiare is a hundredth of an are, which makes it exactly one square meter. The unit is nearly extinct in English but very much alive in the Italian catasto terreni, the land register run by the Agenzia delle Entrate, where the surface of an agricultural parcel is recorded in hectares, ares and centiares.
The format on a visura catastale looks like ha 12 a 34 ca 56. That is 12 hectares plus 34 ares plus 56 centiares, which comes to 123,456 square meters.
Read the three figures straight through as digits and you get 123456. That isn't a coincidence and it isn't a trap: because each unit is exactly a hundred of the next one down, the three fields are the square-meter figure split into pairs of digits. The system is built that way on purpose. What does trip people up is assuming the middle field is a decimal fraction of a hectare, which it isn't.
Most English-language converters omit the are entirely, which is why an Italian parcel can be hard to read with an English tool. It is a field above.
There is only one acre now
The US survey acre was defined on the US survey foot and differed very slightly from the international acre. NIST and NOAA deprecated that foot on 31 December 2022, and the same Federal Register notice redefined the acre, chain, link, rod, furlong and fathom on the international foot.
Since 1 January 2023 there is one acre in official US use, and it is the one this tool uses. The survey versions survive only for legacy state plane coordinate systems.
Common questions
How many acres are in a hectare?
A hectare is 2.4710538 acres. A hectare is exactly 10,000 square meters and an acre is exactly 4,046.8564224 square meters, so the ratio is exact rather than rounded. Going the other way, an acre is 0.40468564 hectares.
What is an are, and why does it appear on European land listings?
An are is 100 square meters, a hectare is 100 ares, and a centiare is one square meter. The Italian land register records parcel areas in all three, in the format ha 12 a 34 ca 56, which is 123,456 square meters. Because each unit is exactly a hundred of the next, those figures read straight through as the square-meter total. Most English-language converters leave the are out entirely.
Is the acre used here the US survey acre?
No, and since 1 January 2023 there is only one acre in official US use. The US survey acre was defined on the US survey foot, which NIST and NOAA deprecated on 31 December 2022. The same notice redefined the acre on the international foot, which is what this tool uses.
Why is an acre 43,560 square feet?
The acre comes from a strip one chain wide by one furlong long. A chain is 66 feet and a furlong is 660 feet, and 66 multiplied by 660 is 43,560. The awkward number is a survival of that shape rather than an arbitrary choice.
Sources
- Centiare. Reference on the Italian catasto terreni, source for the hectare, are and centiare format used on a visura catastale and the worked example ha 12 a 34 ca 56 equalling 123,456 square meters.
- NIST Guide to the SI, Appendix B. Source for every factor above.
- U.S. Survey Foot: Frequently Asked Questions. NIST. Source for the 31 December 2022 deprecation and the redefinition of the acre on the international foot.