Area calculator
The area of common shapes, with the formula shown
Choose a shape and a unit, then type the sizes. The example is a triangle with a 6 m base and a 4 m height.
–
- Square feet
- –
- Square metres
- –
- Square inches
- –
- Square yards
- –
- Acres
- –
- Hectares
- –
A measurement from the sizes you typed. No waste allowance applies here. Check anything covered by a building code, or that you will pay for, against your own measurements.
The formulas
- Rectangle: length x width.
- Triangle, base and height: base x height / 2. The height is measured at right angles to the base, not along a sloping side.
- Triangle, three sides (Heron's formula): with s = half the perimeter, area = √(s(s − a)(s − b)(s − c)). The longest side must be shorter than the other two added together, or there is no triangle.
- Circle: π x radius², where the radius is half the diameter and π is 3.14159...
- Trapezoid: (top + bottom) / 2 x height, for a shape with two parallel sides.
- Ellipse: π x (length / 2) x (width / 2), using the full length and width of the oval.
Units
All sizes must be in the same unit. The answer comes out in that unit squared, then it is converted. The conversions are exact: 1 ft is 0.3048 m, so 1 sq ft is 0.09290304 m².
Worked example
A triangle with a 6 m base and a 4 m height: 6 x 4 / 2 = 12 m². In square feet that is 12 / 0.09290304 = 129.17 sq ft. With three sides of 3, 4 and 5 m, Heron's formula gives s = 6 and √(6 x 3 x 2 x 1) = 6 m².
For whole rooms, the square footage calculator adds several areas together. For land, use the acreage calculator.
Defaults and where they come from
Every default is only a starting point. Change any box to match what you are buying or building.
| Default | Value | Source |
|---|---|---|
| Conversions | 1 in = 2.54 cm; 1 ft = 0.3048 m; 1 yd = 0.9144 m; 1 acre = 4,046.86 m²; 1 hectare = 10,000 m² | Exact definitions (international yard and pound, 1959). |
| Waste allowance | None | This page measures area only. |