Area Calculator
Pick a shape, type in its measurements and get the area right away. This calculator covers ten common shapes, from a simple rectangle to a circular sector, and updates the result as you type.
How to use the area calculator
- Choose the shape you want to measure, such as a circle, rectangle or triangle.
- Enter the dimensions the shape needs, for example a radius, or a width and height.
- Read the area in the result card, which updates as you change the numbers.
Examples
Area of a rectangle
width = 3, height = 4
Area = 12
Area of a circle
radius = 2
Area ≈ 12.5664 (4 x pi)
Area of a triangle from three sides
sides a = 3, b = 4, c = 5
Area = 6
Frequently asked questions
Which shapes can this area calculator handle?
Ten of them: circle, square, rectangle, triangle (base and height), triangle from three sides, trapezoid, parallelogram, ellipse, circular sector and rhombus. Pick one and the right inputs appear.
What are the area formulas used here?
Circle pi x r squared, square side squared, rectangle width x height, triangle ½ x base x height, trapezoid ½ x (a + b) x height, parallelogram base x height, ellipse pi x a x b, sector (angle / 360) x pi x r squared, and rhombus ½ x d1 x d2.
How do I find a triangle's area if I only know the three sides?
Use the three-sides mode, which applies Heron's formula. It works out the semi-perimeter s = (a + b + c) / 2, then the area is the square root of s(s − a)(s − b)(s − c). The three lengths must form a real triangle.
What units does the area come out in?
Whatever units you put in, squared. If you enter centimetres, the area is in square centimetres; if you enter inches, it is square inches. The tool does not assume any unit, so keep your inputs consistent.
Why do I get an error for some triangle side lengths?
A triangle can only exist when the sum of any two sides is greater than the third side. Lengths like 1, 1 and 5 break that rule, so no triangle and no area exist, and the calculator flags it.
Is my data sent anywhere?
No. Every calculation runs in your browser, so the measurements you type are never uploaded, logged or stored.
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