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Circle Calculator
Enter any one value to calculate radius, diameter, area, and circumference.
Radius (r)
5
Diameter (d)
10
Area (A = πr²)
78.539816
Circumference (C = 2πr)
31.415927
Key formulas
A = πr²
C = 2πr
d = 2r
r = C / (2π)
r = √(A/π)
C = πd