How to use the acreage calculator
Choose the shape that best matches your land and enter the side lengths in feet, yards or metres. Most lots are close to a rectangle. For a lot with four unequal sides, measure all four and one diagonal, corner to corner; the calculator splits the lot into two triangles along that diagonal and adds them up. That's the same way surveyors break down irregular parcels.
A plot with more than four sides can be split the same way: draw diagonals from one corner to make triangles, run each triangle here using three sides, and add the acres.
The formulas
acres = square feet ÷ 43,560
rectangle: length × width
trapezoid: (side 1 + side 2) ÷ 2 × distance between them
triangle from three sides (Heron): √(s(s−a)(s−b)(s−c)), where s = (a+b+c) ÷ 2
Worked example: a 660 × 330 ft field
- Area: 660 × 330 = 217,800 ft².
- Acres: 217,800 ÷ 43,560 = 5 acres exactly.
- Hectares: 5 ÷ 2.471 = 2.02 ha.
660 ft is a furlong, the old length of a plowed furrow, and an acre was a strip one furlong long and one chain (66 ft) wide. That's why the numbers come out so neatly.
Why four sides aren't enough
Take a 300 × 300 ft square: 2.07 acres. Push two corners so it leans into a diamond and every side is still 300 ft, but the area shrinks toward zero. Real lots behave the same way. If you only have four side lengths, the area could be anything up to the maximum, so the calculator asks for a diagonal. Your deed or plat usually lists the bearings and distances needed to work it out precisely.
Acre conversions
| 1 acre equals | |
|---|---|
| Square feet | 43,560 |
| Square yards | 4,840 |
| Square metres | 4,046.86 |
| Hectares | 0.4047 |
| Square miles | 1/640 |
Tips for measuring land
- Use your county's GIS map or plat for a quick check. Most counties publish parcel maps with dimensions.
- A measuring wheel is accurate to within a percent or so over open ground. Pacing is fine for a rough idea.
- Measure horizontally. Acreage is the flat, map area. On a slope, a tape laid on the ground reads long.
- For buying, selling or fencing to the line, use the survey. Calculators can't tell you where the boundary actually is.
Questions people ask
How many square feet are in an acre?
43,560. An acre is also 4,046.86 square meters, 4,840 square yards or 0.4047 hectares.
How do I calculate acreage of a lot?
Multiply length by width in feet to get square feet, then divide by 43,560. A lot 660 ft by 330 ft is 217,800 square feet, which is exactly 5 acres.
How big is one acre?
If it were square, about 208.7 ft on each side. A US football field without the end zones (300 × 160 ft) is about 1.1 acres.
Can I calculate acreage from four side lengths?
Not exactly. Four sides alone don't fix the shape: the same four lengths can enclose very different areas as the corners lean. Measure one diagonal as well, and this calculator splits the plot into two triangles and gets the exact area.
How do I convert hectares to acres?
Multiply hectares by 2.471. One hectare (10,000 square meters) is 2.471 acres.
Sources and assumptions
- NIST Handbook 44, Appendix C: 1 acre = 43,560 ft² = 4,046.873 m² (US survey) / 4,046.856 m² (international)
- Four-sided plots use Heron's formula on the two triangles either side of the measured diagonal.
- For legal boundaries or a sale, rely on a licensed survey, not a calculator.
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.