Annulus Calculator
Calculate the area of an annulus (ring) from its outer and inner radii.
Formula: A = π × (R² − r²)
About Annulus Calculator
Annulus Calculator is a free online calculator that gives you an instant, accurate result as you type. Calculate the area of an annulus (ring) from its outer and inner radii.
The calculation uses the standard formula A = π × (R² − r²) and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
An annulus is the region between two concentric circles — the shape of a washer or a CD.
Frequently Asked Questions
Is Annulus Calculator free to use?
Yes. Annulus Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (A = π × (R² − r²)) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
What if the inner radius is larger than the outer radius?
That is not a valid annulus. The outer radius R must be greater than the inner radius r, otherwise the area would be negative.
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