How to use this calculator
- Enter or choose plot shape.
- Enter or choose lengths in.
- The area updates as you type. Use Copy result or Share to keep it.
Method
Rectangle: L × W; Triangle (Heron): √(s(s−a)(s−b)(s−c)), s = (a+b+c) ÷ 2; Four sides: two Heron triangles sharing the diagonal; Coordinates (shoelace): ½ |Σ (xᵢyᵢ₊₁ − xᵢ₊₁yᵢ)|
- a, b, c
- side lengths of a triangle
- xᵢ, yᵢ
- corner coordinates in order around the plot
Worked example
- Area = 30 m × 20 m = 600 m².
- In square feet: 600 ÷ 0.09290304 = 6,458.35 sq ft.
- In hectares: 600 ÷ 10,000 = 0.06 ha; in acres: 600 ÷ 4,046.856 = 0.1483 acres.
A 30 m by 20 m plot is 600 m², about 6,458 sq ft or 0.148 acres.
What the result means
For a legal boundary, rely on the surveyed area on the title or plan. This tool is for checking measurements and comparing plots.
Assumptions and limits
- The plot is treated as flat; areas are horizontal (plan) areas.
- Sides are straight lines between corners.
- Curved boundaries and sloping ground need a survey; the four-sides method needs the diagonal, because four sides alone do not fix the shape.
Questions
Why do I need a diagonal for a four-sided plot?
Four side lengths alone can form many different shapes with different areas. The diagonal splits the plot into two triangles whose areas are fixed by their sides.
How do I get coordinates?
Pick one corner as 0, 0 and measure each other corner’s distance east (x) and north (y) from it, or read them from a site plan or GPS survey in metres.