How to use this calculator
A circle is fully determined by its radius.
The method
Area = πr²; Circumference = 2πr
Enter your values in the labeled fields and choose Calculate. The result panel shows the answer and supporting values when useful.
WORKED EXAMPLE INPUT
Radius: 5
Select Calculate to evaluate these example values.
Scope and limitations
Results assume Euclidean geometry and the radius is nonnegative.
Common questions
Can I use different units?
Use consistent units unless this page is a unit converter. The result follows the units implied by the inputs.
Are results exact?
Displayed values may be rounded. Keep extra precision for important follow-up calculations.
Methods & verification
Formulas use standard mathematical definitions and fixed unit factors where applicable. See our methodology for numerical conventions, rounding, privacy, and limitations.