Annulus (Ring) Table: Ring area by Outer radius (R)
Reference table of ring area for Annulus (Ring) across a range of outer radius (r) values — exact, engine-computed figures you can read off at a glance.
Annulus (Ring) Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Ring area
122.5221
- Ring width
- 3.0000
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Annulus (Ring) Calculator
The Annulus (Ring) Calculator works out your ring area, along with 1 related figure in an instant. Enter outer radius (r) and inner radius (r) and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the outer radius (r).
- Enter the inner radius (r).
- Read off your ring area, together with ring width — the calculator updates automatically, with no button to press.
Formula
The Annulus (Ring) Calculator uses the formula:
Ring area = 3.141592653589793 × (Outer radius (R) ^ 2 - Inner radius (r) ^ 2)
Worked example
For example, with outer radius (r) of 8 units and inner radius (r) of 5 units, the ring area is 122.5221.
| Outer radius (R) | 8 units |
|---|---|
| Inner radius (r) | 5 units |
| Ring area | 122.5221 |
|---|---|
| Ring width | 3.0000 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Radius
- The distance from the centre of a circle or sphere to its edge.
- Area
- The amount of two-dimensional space a shape covers, measured in square units.
Frequently asked questions
An annulus is the ring-shaped region between two circles that share the same centre, like a washer or a CD.
Subtract the inner circle's area from the outer circle's area: A = π(R² − r²). For R = 8 and r = 5 the area is about 122.52 square units.
The width is simply the outer radius minus the inner radius. For R = 8 and r = 5 the ring is 3 units wide.
No. The inner radius must be smaller than the outer radius, otherwise there is no ring.
The Annulus (Ring) Calculator uses the formula: Ring area = 3.141592653589793 × (Outer radius (R) ^ 2 - Inner radius (r) ^ 2). For example, with outer radius (r) of 8 units and inner radius (r) of 5 units, the ring area is 122.5221.
Enter the outer radius (r). Enter the inner radius (r). Read off your ring area, together with ring width — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Annulus (Ring): Formula, Steps & Examples
Learn how to calculate Annulus (Ring) — the formula explained step by step, with worked examples and a free calculator to check your answer.