Pick a shape, enter its dimensions, get the area — and the perimeter where the shape has one worth quoting.
| Shape | Area |
|---|---|
| Rectangle | length × width |
| Triangle | ½ × base × height |
| Circle | πr² |
| Trapezoid | ½ × (a + b) × height |
| Parallelogram | base × height |
| Ellipse | πab (semi-axes a and b) |
| Sector | πr² × (angle ÷ 360) |
This is the single most common mistake. For a triangle or parallelogram, the height is the perpendicular distance from the base to the opposite vertex or side — not the length of a slanted side. On a leaning parallelogram the slanted side is longer than the height, and using it inflates the area.
The give-away is that a parallelogram and a rectangle with the same base and the same perpendicular height have exactly the same area, however far the parallelogram leans. Shearing a shape sideways does not change how much surface it covers.
Area is always in square units. Converting between them trips people up because the conversion factor gets squared too: one metre is 100 centimetres, but one square metre is 10,000 square centimetres, not 100. One square foot is 144 square inches, not 12.
The perpendicular height from the base to the opposite vertex, not the length of a sloping side. If you only know the three side lengths, use the Triangle Calculator instead, which applies Heron’s formula and needs no height.
Because area needs only the base and height, while the perimeter needs every side length — information this shape selector does not ask for. The Triangle Calculator takes all three sides and returns the perimeter.
Multiply by 10.7639. Take care with any area conversion: the linear factor gets squared, so 1 m = 3.28084 ft becomes 1 m² = 10.7639 ft².
A wedge of a circle, like a slice of pie, defined by a radius and the angle at the centre. Its area is the full circle’s area scaled by the fraction of 360° the angle covers.
For circle-specific work use the Circle Calculator, and for three dimensions the Volume Calculator and Surface Area Calculator. Working from three side lengths? The Triangle Calculator handles that. For flooring and materials, see the Unit Converter.