Annulus Area Calculator

About this calculator

This calculator finds the area of an annulus — a flat ring shape formed by two concentric circles — using A = π(R² − r²), where R is the outer radius and r is the inner radius: essentially the area of the whole outer circle minus the area of the inner circle it excludes. It's a direct extension of the standard circle-area formula, applied twice and subtracted.

Mechanical and manufacturing engineers use it to calculate the cross-sectional area or material needed for washers, gaskets, pipes, and tubing; landscapers and garden designers use it to plan circular borders or walkways that ring a fountain or flower bed; and geometry students use it as a standard composite-shape problem combining two circle-area calculations. Enter the outer and inner radii to get the annulus area.