Area of an Annulus Calculator

Summary

Enter the outer and inner radii to instantly compute the area of an annulus using A = π(R² − r²).

How it works

1. Enter the outer radius (R) — the distance from the center to the outer edge.
2. Enter the inner radius (r) — the distance from the center to the inner edge.
3. Choose the unit of measurement (mm, cm, m, in, ft).
4. The calculator applies A = π(R² − r²) and displays the result instantly.
5. Copy the result or swap the unit without re-entering values.

Use cases

• Calculate material needed to cut a washer or gasket.
• Find the cross-sectional area of a hollow pipe or tube.
• Determine paint or flooring coverage for ring-shaped surfaces.
• Verify engineering drawings involving circular cutouts.
• Solve geometry homework involving concentric circles.
• Estimate annular area in optical or lens design.

Frequently Asked Questions