Circle Calculator
Enter a circle's radius to calculate its area, circumference and diameter.
Formula
Area = πr². Circumference = 2πr. Diameter = 2r.
Example
A circle with radius 5 has an area of about 78.54 and a circumference of about 31.42.
Frequently Asked Questions
- What if I only know the diameter?
- Divide the diameter by 2 to get the radius, then enter that.
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