Annulus Calculator
An annulus is the ring-shaped region between two concentric circles. Enter both radii to get the ring's area, width, and circumferences.
Inputs explained
- Outer radius (R) — Radius of the larger circle. Must be greater than the inner radius.
- Inner radius (r) — Radius of the smaller (hole) circle.
How to use it
- Fill in the fields above — each input has a hint describing exactly what to enter
- Press Calculate to get your result instantly, right on this page
- Copy the result, save the tool to favorites, or share and embed it anywhere
Understanding the result
Example: With R = 5 and r = 3, the annulus area is π(25 − 9) ≈ 50.27 square units.
Frequently asked questions
What happens if I enter an inner radius larger than the outer radius? The inner radius must be smaller than the outer radius since it defines the hole inside the ring; entering a larger inner radius describes an invalid shape and will produce a nonsensical or negative area.
Does the annulus calculator give two different circumference values? Yes, it reports the circumference of both the outer circle and the inner circle separately, since each boundary of the ring has its own perimeter length.
Is the Annulus Calculator free to use? Yes — it is completely free, with no sign-up, no download and no usage limits. You can use it as often as you need.
Is my data private? Yes. The calculation runs entirely in your browser — the values you enter are never sent to our servers, stored or shared with anyone.
What information do I need? Just the following: Outer radius (R), Inner radius (r). Each field includes a hint explaining exactly what to enter.
Can I use it on my phone? Yes — the tool is fully responsive and works on any device, and the same calculator is available in the EasyWorkCalcs mobile app.
Privacy
Everything you enter into the Annulus Calculator is processed entirely in your browser. Nothing is uploaded, stored or shared — your data stays on your device.