Enter any one value (radius, diameter, circumference or area), get the other three.
Enter the radius and select 'Radius'; the area is shown as pi times radius squared. You can also start from the diameter, circumference or area and the calculator derives the rest.
Diameter = 2r, Circumference = 2 pi r, Area = pi r squared. Given any one of these, the calculator solves for the radius first, then computes the others.
Yes, runs entirely in your browser.