Method
Diameter = 2r, circumference = 2πr, and area = πr². Any known measurement is first converted to radius.
Example
A circle with radius 5 m has circumference about 31.416 m and area about 78.54 m².
Limits
Check inputs and units. Important academic, financial or professional decisions should be confirmed against an appropriate source.
Common questions
What does the circle calculator calculate?
Calculate radius, diameter, circumference and area from one value.
Does this circle calculator show its method?
Yes. The result includes the central formula or working needed to check the answer.
Are my values uploaded?
No. The calculation runs in this browser and does not require an account.