Math
Circle Calculator
Enter any one of radius, diameter, circumference, or area — get all four.
Inputs
Circle Calculator
Result
Area
78.539816
- Radius
- 5
- Diameter
- 10
- Circumference
- 31.415927
How it's calculated
A = π r². C = 2π r. d = 2r.
Common questions
How precise is π here?
We use JavaScript's Math.PI (about 15 significant digits) — more than enough for any real-world drawing.
Can I go from area back to radius?
Yes. r = √(A / π). Pick “Area” as the known value and enter it.
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