How this instrument works
The acre is a survivor from medieval English farming: originally the area a yoke of oxen could plough in a day, later fixed as one chain by one furlong — 66 feet by 660 feet. Multiply those and you get 43,560 square feet exactly, which is why such an awkward-looking number sits at the centre of American land measurement to this day.
Because the international foot has been defined as exactly 0.3048 metres since 1959, the acre inherits an exact metric value too: 4,046.8564224 square metres. The conversion this sheet performs is therefore not an approximation at any step — dividing by 43,560 is the whole of it, and the long decimal in the factor is simply that division written the other way round.
Lot sizes, farm parcels, and building footprints in the United States are still quoted in whichever unit suits the audience: a realtor lists a suburban plot in square feet to make it sound generous, while the same parcel appears in acres on the county record. Being able to move between them quickly is the difference between comparing properties and guessing at them.
- Enter the area in square feet — a lot, a field, or a building footprint.
- Read the equivalent in acres directly beneath, to six decimal places.
- Open the working block to see the exact factor applied to your figure.
Worked example — the one-acre plot
A rectangular parcel measures 43,560 square feet. Multiply by 2.29568411387 × 10⁻⁵ — or equivalently divide by 43,560 — and the answer is exactly 1.0 acre. That clean result is the definition itself doing the work, which makes it the ideal check that any acreage tool is honest.
Scale it to something more familiar: a suburban lot of 8,712 square feet is one fifth of an acre, and a standard American football field, excluding the end zones, covers 48,000 square feet or about 1.102 acres. Those two figures give you a mental yardstick for reading any listing quickly.
Questions
Why is an acre 43,560 square feet rather than a round number?
It descends from the medieval acre of one chain by one furlong: 66 feet by 660 feet. That rectangle was a practical day's ploughing for an ox team, not a decimal convenience. When the units were later standardised the shape was dropped but the area was preserved, leaving the number we still use.
Is this conversion exact or rounded?
Exact. Since 1959 the international foot has been exactly 0.3048 metres, so the acre is exactly 4,046.8564224 square metres and exactly 43,560 square feet. The multiplier displayed here is that ratio inverted and shown to twelve significant figures; only the final display is rounded.
Does the shape of the land matter?
No. An acre is a measure of area alone, so a long thin strip and a perfect square of the same area are both one acre. If you have length and width in feet, multiply them first and enter the product here. For irregular parcels, a surveyor's stated area is the figure to use.
What is the difference between a US survey acre and an international acre?
They differ by about two parts per million, because the US survey foot was very slightly longer than the international foot. The survey foot was officially retired at the end of 2022, so current work uses the international definition applied here. The gap only matters across very large tracts.
How many acres is a hectare?
One hectare is 10,000 square metres, which is about 2.471 acres, so an acre is roughly 0.405 hectares. Where an acre descends from ploughing, the hectare is a purely metric invention — a square 100 metres on each side — and most of the world outside the United States uses it for land.