Area Calculator
Area of any shape.
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Geometry
Circle Calculator
Enter the radius to get a circle’s area, circumference and diameter.
Area
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From the radius.
| Circumference | — |
|---|---|
| Diameter | — |
| Radius | — |
| — |
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Enter your figures above to see the step-by-step working.
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How the Circle Calculator Works
A circle is defined entirely by its radius, so from that single measurement you can find everything else. This calculator takes the radius and returns the area (πr²), the circumference — the distance around (2πr) — and the diameter, which is twice the radius.
If you know the diameter instead, halve it to get the radius. Keep the radius in whatever unit you like; area comes out in that unit squared and circumference in the plain unit.
area = πr² · circumference = 2πr · diameter = 2r
Frequently Asked Questions
How do you find the area of a circle?
Square the radius and multiply by π (about 3.1416). A radius of 5 gives an area of about 78.54.
What is the circumference of a circle?
The distance around it: 2πr, or π times the diameter. For a radius of 5 that’s about 31.42.
How do I get the radius from the diameter?
Divide the diameter by two — the radius is half the diameter.
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Surface area of a solid.
Open →Area of a Circle Calculator
Area from radius.
Open →Triangle Area Calculator
Triangle area.
Open →