Find a circle’s area, circumference and diameter from the radius.
Calculated locally in your browser.
Understanding your result
Results use the value of π and are rounded for display.
Formula and method
Area = π r², circumference = 2 π r, diameter = 2 r.
Worked example
A radius of 5 gives an area of about 78.54 and a circumference of about 31.42.
How to use this tool
- Enter the radius.
- Read the area, circumference and diameter.
Common mistakes to avoid
- Entering the diameter where the radius is expected.
About the Circle Calculator
Enter a circle’s radius to find its area, circumference and diameter.
Frequently asked questions
How do I use the diameter instead?
Halve the diameter to get the radius, then enter it.