Circle from Area Calculator

About this calculator

This calculator works Circle Area = π·r² backward: given the area, it solves for radius as r = √(A/π), then derives diameter (2r) and circumference (2πr or π·d) from that radius — the reverse direction of the more commonly known area calculation.

Students checking geometry homework where area is given but radius is asked for, engineers and designers sizing a circular part or opening to hit a target area (like a vent, gasket, or pipe cross-section), and land or landscaping planners converting a plot's area into a circular boundary radius use this. Enter the area to get the radius, diameter, and circumference.