Circle Calculator
Enter any one circle measurement — radius, diameter, circumference, or area — and calculate all the others instantly.
Circle Properties
Circle formulas — knowing any one measurement lets you find all others.
From radius (r):
Diameter = 2rCircumference = 2πrArea = πr²
From diameter (d):
Radius = d / 2Circumference = πdArea = π(d/2)²
From circumference (C):
Radius = C / (2π)Diameter = C / πArea = C² / (4π)
From area (A):
Radius = √(A / π)Diameter = 2√(A / π)Circumference = 2π√(A / π)
Quick reference:
| Radius | Diameter | Circumference | Area |
|---|---|---|---|
| 1 | 2 | 6.28 | 3.14 |
| 5 | 10 | 31.42 | 78.54 |
| 10 | 20 | 62.83 | 314.16 |
| 25 | 50 | 157.08 | 1,963.50 |
π (pi) ≈ 3.14159265358979…
Enter any single value below and the calculator will find the rest.