Formula
Rectangle: A = l × wTriangle: A = ½ × b × hCircle: A = πr²Trapezoid: A = ½(a + b) × hEllipse: A = π × a × bParallelogram: A = b × h How it works
Area is the amount of flat surface a shape covers, measured in square units. A rectangle 8 m long and 5 m wide covers 40 squares that are each 1 m on a side, so its area is 40 m².
Many shapes reduce to the rectangle. A parallelogram can be cut and slid into a rectangle with the same base and height. A triangle is half of a parallelogram, which is where the ½ comes from. A trapezoid’s area uses the average of its two parallel sides times its height.
For triangles, parallelograms and trapezoids, the height must be perpendicular to the base — not the length of the slanted side. Choose the units of your measurements and the units you want for the answer independently; the calculator converts between them, for example from feet to square metres.
Frequently asked questions
How do I find the area of an irregular shape?
Split it into rectangles, triangles and circles, find each area separately, then add them up (or subtract the area of any holes).
How many square feet are in a square metre?
About 10.764. Because area is two-dimensional, the conversion factor is the length factor squared: 3.2808² ≈ 10.764.
What are the semi-axes of an ellipse?
They are half the longest width and half the shortest width, measured from the centre. For a circle both semi-axes equal the radius, and the formula πab becomes πr².