Area Calculator
Compute the area of common 2D shapes by selecting a shape and entering its dimensions.
Example
For a trapezoid with parallel sides a = 6 and b = 10, and height h = 4:
Area = 1/2 x (a + b) x h
= 1/2 x (6 + 10) x 4
= 1/2 x 16 x 4
= 32
How it works
Choose a shape from the dropdown to reveal its inputs, then type the dimensions. The area updates live using each shape's standard formula.
Good to know
The Area Calculator works out the surface area of six common 2D shapes — rectangle, triangle, circle, trapezoid, parallelogram, and ellipse — from the measurements you type in. It is built for students checking homework, DIYers estimating paint, flooring, or fabric, and anyone who needs a quick, reliable area without remembering each formula. Because it runs entirely in your browser, it is also handy when you want a calculation that involves no sign-up and no data leaving your device.
Reach for it whenever a problem reduces to "how much surface does this cover?" — sizing a rug for a room, working out turf for a garden bed, finding the cross-section of a beam, or solving a geometry exercise. Switch shapes from the dropdown and only the relevant inputs appear, so you are never guessing which measurements a given formula needs.
Read the big number as the area expressed in whatever unit you entered, squared: enter centimetres and you get square centimetres; enter feet and you get square feet. The panel also echoes the shape and the exact formula it applied (for example pi x r^2 for a circle), which lets you confirm the tool used the calculation you expected. The result is rounded to six decimal places for display.
A practical caveat: the answer is only as good as your measurements, and the most common mistake is using a slanted side instead of the perpendicular height for triangles, parallelograms, and trapezoids. Keep every input in one consistent unit before reading the result, and if your shape is irregular, split it into these basic shapes, calculate each piece, and add the areas together.
Frequently asked questions
What do the two values mean for an ellipse?
Enter the two semi-axes (half of each full axis). The area is pi x a x b, so a circle is just the special case where a equals b (giving pi x r^2).
Which height should I use for a triangle or parallelogram?
Use the perpendicular height measured at a right angle to the base you entered, not the slanted side length. Otherwise the area will be too large.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is it free?
Yes, completely free with no sign-up and no limits.
People also ask
What is the formula for the area of each shape in this calculator?
Rectangle is width x height, triangle is 1/2 x base x height, circle is pi x radius squared, parallelogram is base x height, trapezoid is 1/2 x (a + b) x height, and ellipse is pi x semi-axis a x semi-axis b.
How do I convert the area result to a different unit?
Area units scale by the square of the length conversion. For example, 1 square foot equals 144 square inches (12 x 12), and 1 square metre equals 10,000 square centimetres (100 x 100).
What is the difference between a diameter and a radius for the circle option?
The radius is the distance from the centre to the edge, and the diameter is the full width across the centre, so the radius is half the diameter. This calculator asks for the radius, so divide a measured diameter by 2 before entering it.
How do I find the area of an irregular or composite shape?
Break the shape into simpler pieces such as rectangles and triangles, calculate the area of each piece separately, then add them together. For a shape with a hole, subtract the inner area from the outer area.
Why does my triangle area come out too large?
This usually happens when the slanted side length is entered instead of the perpendicular height. The height must be measured at a right angle from the base to the opposite vertex, not along the sloping edge.
What units should I enter into the area calculator?
You can use any unit (inches, centimetres, metres, feet) as long as every dimension uses the same one. The result is reported in that unit squared.
Is a square calculated the same way as a rectangle here?
Yes. A square is a rectangle whose sides are equal, so select Rectangle and enter the same value for both width and height.
What are the semi-axes of an ellipse?
The semi-axes are half the length of the ellipse's longest and shortest full diameters. Enter each as a separate value, a and b; when a equals b the ellipse becomes a circle.
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