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Results
Enter your dimensions above and the results appear here.
About the Ring (Annulus) Calculator
The ring (annulus) calculator is a free online tool: area between two concentric circles. Enter outer radius (R) and inner radius (r) and the results update instantly, alongside a labelled diagram so you always know which measurement goes where.
Choose your input unit (mm, cm, m, km, in, ft or yd) and optionally show the results in a different one: lengths, areas and volumes are converted correctly. Every answer shows the formula behind it, and the calculation runs in your browser, so nothing is uploaded.
Ring (Annulus) Calculator example
Outer radius (R) = 8 cm
Inner radius (r) = 5 cmArea = 122.5221 cm²
Ring width = 3 cm
Outer circumference = 50.2655 cm
Inner circumference = 31.4159 cm
Total edge length = 81.6814 cmHow to use the Ring (Annulus) Calculator
- Pick the unit your measurements use. All dimensions must share the same unit.
- Enter outer radius (R) and inner radius (r). Focus a field to highlight the matching label on the diagram.
- Read the results as you type. The largest card is the main answer; the others are the related measurements.
- Copy a single value, copy everything, or share a link that keeps your inputs.
Ring (Annulus) Calculator FAQ
What formulas does the ring (annulus) calculator use?
A = π(R² − r²); Width = R − r; Edge = 2π(R + r).
Can I use different units?
Yes. Pick the input unit and, if you like, a different output unit. Area results are shown in squared units and volumes in cubed units.
Is this ring (annulus) calculator free and private?
Yes. It is free with no sign-up, and calculations happen on your device, so your numbers are never sent to a server.
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