Circle Calculator
Calculate area, circumference, diameter, and radius of a circle. Enter any one value to find all others instantly.
About the Circle Calculator
This calculator computes the four key properties of a circle: radius (r), diameter (d = 2r), circumference (C = 2πr), and area (A = πr²). Enter any one value and the calculator solves for the other three using π ≈ 3.14159265.
Formulas: Area = π × r², Circumference = 2 × π × r, Diameter = 2 × r
Enter Circle Value
Calculate From
Radius
units
Results
Radius (r)
5
Diameter (d)
10
Circumference (C)
31.4159
Area (A)
78.5398
Formula Used: A = π × r² = 3.14159 × 25 = 78.5398
Circle Formulas & Examples
1
Area
A = π × r²
If r=5: A = 3.14159 × 25 = 78.54
2
Circumference
C = 2 × π × r
If r=5: C = 2 × 3.14159 × 5 = 31.42
3
Diameter
d = 2 × r
If r=5: d = 10
4
Radius from Area
r = √(A/π)
If A=78.54: r = √25 = 5