Circle Calculator
Area, circumference and diameter from any one value.
Reviewed by James Whitfield · How we check our maths
Your values
ⓘ Live results
Results
- Area
- 78.539816
- Circumference
- 31.415927
- Radius
- 5
- Diameter
- 10
- Sphere volume with this radius
- 523.598776
Working
- 1A = π × 5² = 78.5398
Quick answer
Circle area is πr² and circumference is 2πr, so any one measurement determines all the others.
The formula
A = πr², C = 2πr
Worked example
Worked example
Using the values the calculator loads with.
Inputs
- What do you know?Radius
- Value5
Result
- Area78.539816
- Circumference31.415927
- Radius5
- Diameter10
- Sphere volume with this radius523.598776
How to use the Circle Calculator
- 1Choose which measurement you already have.
- 2Enter its value.
- 3Read every other circle property.
Frequently asked questions
Why is π irrational?
Its decimal expansion never repeats or terminates — proved by Lambert in 1761.
How do I find area from circumference?
Divide circumference by 2π to get the radius, then square it and multiply by π.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error