Area Calculator
Area of any shape.
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Geometry
Area of a Circle Calculator
Enter the radius or diameter to get the area of a circle.
Area of the circle
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πr².
| Radius | — |
|---|---|
| Diameter | — |
| Circumference | — |
| — |
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Enter your figures above to see the step-by-step working.
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How the Area of a Circle Calculator Works
The area of a circle is π times the radius squared (πr²). Enter the radius — or switch to diameter and the calculator halves it for you — and it returns the area, along with the diameter and circumference.
π (pi) is about 3.14159, the ratio of any circle’s circumference to its diameter. Because the radius is squared, doubling the radius quadruples the area.
area = π × radius²
Frequently Asked Questions
What is the formula for the area of a circle?
Area = πr² — pi (about 3.1416) multiplied by the radius squared.
How do I find the area if I only know the diameter?
Halve the diameter to get the radius, then use πr². This calculator does that automatically if you pick “diameter”.
Why is the radius squared?
Area grows with the square of the radius, so a circle twice as wide has four times the area.
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