Circle Calculator
Enter a radius, diameter, circumference or area and get the other three circle measurements instantly.
Enter a radius, diameter, circumference or area and get the other three circle measurements instantly.
Formula
Diameter = 2r. Circumference = 2 x pi x r. Area = pi x r squared.
Example
Radius 5 gives diameter 10, circumference 31.42 and area 78.54.
How to use it
- Choose which measurement you know.
- Enter its value.
- Press Calculate.
- Read the radius, diameter, circumference and area.
Frequently asked questions
Do I have to enter the radius?
No. Enter any one of radius, diameter, circumference or area and the rest are worked out from it.
What value of pi is used?
The full double precision value of pi, with results rounded to two decimals for display.
Can I use other units?
Yes, as long as one unit is used consistently. The outputs are in the same unit, or square units for area.