Radius 5
Diameter 10, circumference ≈ 31.4159, area ≈ 78.5398.
Circle Calculator
Get a circle's radius, diameter, circumference and area from any one of them.
Result
Enter your values and select Calculate to see the result.
Runs in your browser — nothing you enter is sent to a server.
How the Circle Calculator works
Choose which measurement you know — radius, diameter, circumference or area — and enter it. The calculator finds the radius and from it the other three.
Formulas
From the radius r
diameter = 2r; circumference = 2πr; area = πr²
Back to the radius
r = d ÷ 2 = C ÷ 2π = √(A ÷ π)
Examples
From the area
An area of π (about 3.1416) means a radius of exactly 1.
Frequently asked questions
Which value of π is used?
The full double-precision value, 3.141592653589793.
What units does it use?
Any: the lengths come out in your unit and the area in that unit squared.
How do I find the area of a ring?
Subtract the inner circle's area from the outer circle's.
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