Area Calculator Online — Circle, Rectangle, Triangle — Free
Runs 100% in your browser — your files never leave your device.
Square footage for flooring, fabric for a banner, paint coverage for a wall — area questions are constant and the formulas are easy to mix up. Pick a shape, type its dimensions, and read the area instantly. Only the fields the chosen shape needs appear, so there is nothing to configure.
How it works
- 1
Pick the shape
Rectangle, square, circle, triangle, or trapezoid.
- 2
Type the dimensions
Only the measurements the shape needs appear — radius for a circle, base and height for a triangle.
- 3
Read the area
The result updates live as you type, in square units.
About this tool
The shapes it covers
Enter the dimensions and the tool computes the area of rectangles, triangles, circles, trapezoids, and more — the standard formulas applied correctly, with the result in square units of whatever you entered. Pick the shape, fill the fields, read the area.
Units are your responsibility
The formula is unit-agnostic: enter meters and the answer is square meters; enter feet and it is square feet. Mixing units inside one shape is the classic error — convert everything to the same unit first, and remember area scales with the square (twice the length is four times the area).
Checking the answer by scale
Sanity-check every result against a known reference — a soccer pitch is about 7,000 square meters, a parking space about 12. If the computed area of "a bedroom" comes back at 400 square meters, one of the inputs has a unit problem.
Frequently asked questions
What units does the calculator use?
Whatever you enter — the formulas work on pure numbers. The output carries the square of your input unit, so keep every dimension in the same unit.
How do I calculate an irregular shape?
Decompose it: split the shape into rectangles and triangles, compute each, and add the areas. The calculator handles the pieces.
Why does doubling a side quadruple the area?
Area scales with the square of length — a shape twice as long and twice as wide covers four times the space. That nonlinearity is the most common estimation error in scaling.