The region between two concentric circles—a ring. Outer radius R, inner radius r.

Area = π(R² − r²) = π(R − r)(R + r). R and r must be in the same units.

Inner radius must be less than outer radius for a valid annulus.

Online Annulus Calculator

Calculate the area of an annulus (ring) from outer radius R and inner radius r. Area = π(R² − r²).

Outer radius R

Inner radius r

Frequently Asked Questions

What is an annulus?: The region between two concentric circles—a ring. Outer radius R, inner radius r.
What is the formula?: Area = π(R² − r²) = π(R − r)(R + r). R and r must be in the same units.
What if r ≥ R?: Inner radius must be less than outer radius for a valid annulus.

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