Area calculator
Area of a rectangle is length × width; one acre is 43,560 square feet. Pick a shape, or paste a list of coordinates, to get square feet, acres, square meters, and hectares.
Last updated: · Free tool by InsightSpatial
Private by design. This tool runs entirely in your browser. What you enter stays on your device. It is not uploaded to us or stored.
Formulas
- Rectangle: length × width.
- Triangle from three sides (Heron's formula): with s = (a + b + c) ÷ 2, area = √(s (s − a)(s − b)(s − c)).
- Circle: π × (diameter ÷ 2)².
- Four-sided lot: split along diagonal AC into triangles ABC and CDA and add their areas.
- X and Y coordinates (shoelace formula): area = ½ |Σ (xᵢ yᵢ₊₁ − xᵢ₊₁ yᵢ)|.
- Latitude and longitude: the polygon is measured on the WGS 84 ellipsoid with GeographicLib, so the result does not depend on a map projection.
Example: a lot 150 feet by 100 feet is 15,000 square feet. Divide by 43,560 to get 0.344 acres. In square meters, 15,000 × 0.09290304 = 1,393.5 m².
Measuring an irregular lot
Few lots are true rectangles. Split the area into triangles and measure all three sides of each, or walk the boundary with a GPS app and let it compute the area. A phone is typically accurate to a few meters, which can change the area of a small lot by 10% or more; see How to measure land area with your phone for how much it matters.
Questions
How do I calculate square footage?
Multiply length by width in feet. For an L-shaped or irregular area, split it into rectangles and triangles, work out each one, and add them up.
How many acres is my lot?
Divide the square footage by 43,560. A lot 100 feet by 150 feet is 15,000 square feet, or about 0.34 acres.
Why does a four-sided lot need a diagonal?
Four side lengths alone do not fix the shape: the same sides can make a rectangle or a squashed parallelogram with much less area. One diagonal splits the lot into two triangles whose areas are fixed by their sides.
How do I find the area from GPS coordinates?
Choose Coordinates and paste the corners in order around the boundary, one per line. Latitude and longitude are measured on the WGS 84 ellipsoid, the same model GPS uses. You can also paste X and Y coordinates in feet or meters, such as State Plane.
Is this accurate enough for a property survey?
The math is exact, but the result is only as good as your measurements. For legal descriptions or boundary questions, use a licensed land surveyor.