Math
Circle Calculator
Enter the radius, diameter, circumference or area of a circle and get all the others.
Diameter
10
- Circumference
- 31.4159
- Area
- 78.5398
A circle with radius 5 has a diameter of 10, a circumference of 31.4159 and an area of 78.5398.
How it's worked out
- Radius
r5 - Circumference
2 × π × r31.415927 - Area
π × r²78.539816
The formulas
d = 2r · C = 2πr · A = πr²
Worked example
A radius of 5 gives a diameter of 10, a circumference of 31.4159 and an area of 78.5398.
Questions people ask
How do I find the area of a circle?
Multiply π by the radius squared. A circle with a 5 cm radius has an area of 78.54 cm².
How do I find the circumference?
Multiply the diameter by π, or the radius by 2π. A 5 cm radius gives 31.42 cm.
How do I find the radius from the area?
Divide the area by π and take the square root.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem