How it works
Calculate circle area, circumference and diameter from the radius. Do not enter the diameter in the radius field.
A = πr²; C = 2πr; d = 2r
Worked example
Show example inputs and result
Radius: 5.
- Area
- 78.53981634
- Circumference
- 31.41592654
- Diameter
- 10
Questions and answers
Why are some results rounded?
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Are my inputs sent to a server?
The calculator processes inputs in your browser. Its code does not send your values to a server.
Method reviewed: October 8, 2026 · Methods & accuracy