Area Calculator

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Calculate the area and perimeter of a rectangle, triangle, circle, trapezoid, parallelogram or ellipse. Pick a shape, enter the dimensions and get instant results. Free.

w h b h r a b h b h a b
Area – square units
Perimeter –
Enter dimensions in the same unit; area is in square units. The ellipse perimeter uses Ramanujan's approximation. Triangle perimeter needs all three side lengths.

About Area Calculator

The area calculator finds the area and perimeter of six common shapes: rectangle, triangle, circle, trapezoid, parallelogram and ellipse. Pick a shape, enter its dimensions and both results appear instantly — no formula lookup required.

Each shape uses its standard geometry: width × height for a rectangle, ½ × base × height for a triangle, πr² for a circle, and the average of the parallel sides times the height for a trapezoid. The ellipse perimeter uses Ramanujan’s approximation, which is accurate to well beyond practical measuring precision.

Use it for homework, flooring and paint estimates, garden planning or any task where you need square footage of a non-rectangular shape. It is free and runs completely in your browser.

How to use Area Calculator

  1. Select the shape: rectangle, triangle, circle, trapezoid, parallelogram or ellipse.
  2. Enter the dimensions the form asks for, all in the same unit.
  3. For a triangle, add all three side lengths if you also want the perimeter.
  4. Read the area in square units and the perimeter below it.

Frequently asked questions

The area only needs a base and height, but the perimeter is the sum of all three side lengths, so the calculator asks for sides a, b and c to report it.

There is no simple exact formula for an ellipse’s perimeter, so the tool uses Ramanujan’s approximation, which is marked as approximate but is far more precise than any real-world measurement.

Any unit you like — meters, feet, inches — as long as every dimension of the shape uses the same one. The area comes out in that unit squared and the perimeter in the linear unit.

A trapezoid has two parallel sides of different lengths (top a and bottom b), so its area is ½(a + b) × height. A parallelogram’s opposite sides are equal, giving base × height.

Split it into rectangles and triangles, calculate each piece with this tool, then add the areas together. That is the standard approach for L-shaped or angled rooms.
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