Area Calculator
Find the area of common flat shapes.
Formulas for common shapes
- Rectangle: length × width.
- Triangle: base × height ÷ 2.
- Triangle from three sides: Heron’s formula, √(s(s − a)(s − b)(s − c)), where s is half the perimeter.
- Trapezoid: (a + b) ÷ 2 × height.
Examples
An 8 by 5 rectangle has an area of 40. A triangle with base 6 and height 4 has an area of 12. A triangle with sides 3, 4 and 5 has an area of 6. A trapezoid with parallel sides 6 and 4 and a height of 3 has an area of 15.
Area is always in square units, so 40 on a plan measured in metres means 40 square metres. For circles, use the circle calculator.
Frequently asked questions
How do I find the area of a triangle with no height?
Use the three-sides tab. Heron's formula needs only the lengths of the sides.
Why does it say the sides cannot form a triangle?
Each side must be shorter than the other two combined. If not, the sides cannot meet.
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