Formula and method
FormulaArea = πr²; circumference = 2πr.
Both measurements depend on the radius, the straight-line distance from the center to the circle.
Worked example
A radius of 5 gives area 78.5398 and circumference 31.4159.
How to use this calculator
- Enter the values using the labels and units shown.
- Review the live result and supporting details.
- Check the formula, example and assumptions before using the answer.
Assumptions and limits
- Radius and outputs use consistent linear and square units.
Reference
Formula reviewed 2026-07-15