Circle Area Calculator

Circle area from radius or diameter

With radius r, use A = πr². The radius runs from the center to the edge. The diameter d runs through the center from one edge to the other and equals twice the radius.

With a diameter, use A = πd² ÷ 4. The calculator converts diameter to radius before calculating, and uses the full precision of π.

Example: a circle with a 10 ft diameter

The radius is 10 ÷ 2 = 5 ft. Area = π × 5² = 25π, or approximately 78.54 ft² and 7.30 m².

Measure across the center

For a circular tabletop, garden bed or pool surface, measure the widest distance across the center to get the diameter. Selecting radius while entering a diameter makes the calculated area four times too large.

This result covers the surface inside the circle. It is not the circumference, which is the distance around the edge. To calculate water capacity using depth, try the pool volume calculator.

Results are rounded for display. Calculations use unrounded values and international foot-based conversions. Enter actual lengths, rather than squared units.