About this tool
Enter any one of radius, diameter, circumference or area and the other three are computed instantly. It uses pi to relate the values and updates live, entirely in your browser with no uploads.
Frequently asked questions
Which value should I enter?
Any single one — radius, diameter, circumference or area. The moment you type in one field, the other three are filled in for you.
What formulas are used?
Diameter is 2r, circumference is 2πr and area is πr². Entering area or circumference works backwards to find the radius first.