Acreage Calculator
The acreage calculator turns lot dimensions into acres, square feet, square meters and hectares, for rectangular, triangular, circular and irregular four-sided lots.
Acres
- Acres 20,000 square feet divided by 43,560. 100 ft x 200 ft = 20,000 sq ft.
- 0.4591
- Square feet
- 20,000
- Square meters
- 1,858
- Hectares
- 0.1858
- Square yards
- 2,222
- A square of the same area
- 141.4 ft (43.1 m) on each side
- Quarter-acre lots By area alone, at 10,890 sq ft each. Roads, setbacks and the local zoning minimum lot size decide how many lots a parcel can really become.
- 1.84 (1 whole)
- Perimeter
- 600 ft
| Lot size | Square feet | Square meters | Square of side | This lot is |
|---|---|---|---|---|
| 1/8 acre | 5,445 | 506 | 73.8 ft | 3.67x |
| 1/4 acre | 10,890 | 1,012 | 104.4 ft | 1.84x |
| 1/3 acre | 14,520 | 1,349 | 120.5 ft | 1.38x |
| 1/2 acre | 21,780 | 2,023 | 147.6 ft | 0.92x |
| 1 acre | 43,560 | 4,047 | 208.7 ft | 0.46x |
| 5 acres | 217,800 | 20,234 | 466.7 ft | 0.09x |
How the Acreage Calculator works
An acre is 43,560 square feet. That figure is a definition rather than a measurement, and it is the only number this calculation needs: find the area of the lot in square feet and divide by 43,560. A lot 100 feet by 200 feet is 20,000 square feet, which is 0.459 acres, a little under half an acre. A lot 208.7 feet on each side is almost exactly one acre, which is the easiest way to picture one.
The odd number comes from the acre's history as a strip of farmland one furlong long (660 feet) and one chain wide (66 feet). 660 times 66 is 43,560. The shape stopped mattering long ago and the area stayed.
Metric land is measured in hectares. A hectare is 10,000 square meters, a square 100 meters on a side, and it is about 2.471 acres. Because the foot is defined as exactly 0.3048 meters, a square foot is exactly 0.09290304 square meters and every conversion in this calculator is exact up to the final rounding. The US survey foot, retired for new work at the end of 2022, differs from the international foot by about 2 parts per million, under a fifth of a square foot on an acre. Converting areas squares the length factor, which is the common slip: a yard is 3 feet, so a square yard is 9 square feet, not 3.
Rectangles and triangles are straightforward. A rectangle is length times width. A triangle is half the base times the perpendicular height: the distance straight across from the base to the opposite corner, not the length of a sloping side. A circular area, such as an irrigated pivot field, is pi times the radius squared.
Real lots are often four-sided without being rectangles, and this is where most measurements go wrong. Four side lengths are not enough to fix the area of a four-sided shape. The sides are joined at the corners like a hinged frame: push on one corner and the frame leans over into a different shape with the same four sides and a smaller area. A 100 by 200 foot rectangle and a steeply leaning parallelogram with the same sides can differ by nearly all of the rectangle's 20,000 square feet. The usual fix in the field is to measure one diagonal as well. A diagonal splits the lot into two triangles, a triangle is rigid (three sides fix it completely), and Heron's formula gives each triangle's area from its three sides alone. Add the two and you have the lot.
Measure the diagonal inside the lot, from corner A to corner C, going around the corners in order. If the lot has an inward-pointing corner, the diagonal has to start from that corner, because the other diagonal would run outside the boundary. If the numbers cannot form a triangle, with one length longer than the other two combined, no lot has those measurements, and usually something was entered out of order.
A shortcut you will see is to average the opposite sides and multiply the two averages. It is quick and it is always wrong in the same direction: for any four-sided lot that is not a rectangle it overstates the area, sometimes by a lot.
Distances on a survey are horizontal, so a tape laid along a hillside reads longer than the true horizontal distance and inflates the area.
Acreage Calculator FAQ
How many square feet are in an acre?
43,560 square feet exactly. It comes from the historical acre of one furlong (660 ft) by one chain (66 ft). An acre is about 4,046.86 square meters, or 0.4047 hectares.
How do I calculate the acreage of a lot?
Find the area in square feet and divide by 43,560. A rectangular lot is length times width, so 100 ft by 200 ft is 20,000 sq ft, or 0.459 acres. For an irregular four-sided lot, measure the four sides and one diagonal, split it into two triangles and add their areas.
Why do I need a diagonal for an irregular lot?
Because four side lengths do not determine a four-sided shape. The corners act like hinges, so the same four sides can enclose a range of areas from nearly zero up to a maximum. A diagonal splits the lot into two triangles, and a triangle's three sides do fix its area.
How big is a quarter acre?
10,890 square feet, or about 1,012 square meters. As a square it is about 104.4 ft on a side. Half an acre is 21,780 square feet.
How many acres is a hectare?
About 2.471 acres. A hectare is 10,000 square meters, and an acre is 4,046.8564224 square meters exactly, so one hectare is 10,000 / 4,046.8564224 acres.
Is this the legal size of my lot?
No. This is arithmetic on the measurements you enter. A lot's legal boundaries and area come from the deed, the recorded plat or a licensed survey, and those are the figures to rely on for a sale, a permit or a boundary question.