Circle Calculator
From a circle's radius, find its diameter, circumference and area.
Quick answer: enter your details below and click Calculate — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
C
Calculators
Enter your details below.
How to use
- Enter the radius.
- Keep the unit consistent with whatever you are measuring.
- Calculate to see the diameter, circumference and area.
About this tool
Enter the radius, the distance from the centre to the edge. The diameter is twice the radius, the circumference is two times pi times the radius, and the area is pi times the radius squared. One measurement therefore gives you the whole circle.
Frequently asked questions
What is the difference between radius and diameter?
The radius goes from the centre to the edge, while the diameter goes all the way across through the centre, so the diameter is always twice the radius.
What value of pi is used?
The calculation uses the full precision value of pi built into the browser, and the displayed answers are rounded to two decimal places.