Enter any one measurement — radius, diameter, circumference or area — and get the rest.
All four measurements of a circle are mathematically linked through the radius — knowing any single one lets you solve for the radius first (e.g. r = √(Area/π) when area is known), then derive the other three from it.
The calculator rearranges A = πr² to solve for r: r = √(A / π). It then uses that radius to compute the diameter, circumference and confirms the area.
It rearranges C = 2πr to solve for r: r = C / (2π). From there it derives the diameter and area the same way as any other starting measurement.