Circle Calculator
Calculate circle radius, diameter, area, and circumference.
Enter any one value to calculate all circle properties.
How to Do It Manually
All circle measurements stem from the radius (r). Diameter is twice the radius. Circumference and area follow from there.
Diameter = 2r | Circumference = 2πr | Area = πr²
- Identify what you know: radius, diameter, circumference, or area.
- Use the appropriate formula to find the others.
- π ≈ 3.14159265.
Frequently Asked Questions
What is π (pi)?
Pi is the ratio of a circle's circumference to its diameter. It is approximately 3.14159265 and is an irrational number.