Area calculator
Area of a rectangle, triangle, circle, trapezoid and other shapes.
About this calculator
This area calculator works out the area of the most common 2D shapes. Pick a shape, choose a unit and enter its measurements.
The result is shown with the formula used, and converted to square metres, square feet, hectares and acres.
How it works
Each shape has its own formula, shown with the result. All lengths must be in the same unit, and the area comes out in that unit squared.
Last reviewed:
Worked example
- Shape: Rectangle
- Unit: Metres
- Length: 6
- Width: 4
Area: 24 m²
Common questions
How do I find the area of a circle?
Multiply pi (about 3.1416) by the radius squared: A = π × r². If you know the diameter, halve it first to get the radius.
What is the formula for the area of a triangle?
Half the base times the height: A = ½ × b × h. The height is measured at right angles to the base. If you only know the three sides, use the triangle calculator.
How do I find the area of an irregular room?
Split it into rectangles, work out each one and add them up. The square footage calculator does this for you.
The story behind it
Where the idea came from: The Rhind Mathematical Papyrus, copied in Egypt around 1550 BC, includes problems on finding the area of fields.
Ancient surveyors needed to measure land, often after the Nile's floods washed boundaries away. Egyptian and Babylonian scribes worked out rules for rectangles, triangles and even circles, with a value for pi that was close to the real one. The formulas on this page are the refined versions of those early rules.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
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