Just enter the Outer Radius and Inner Radius of the annulus below and click Calculate Area. Use a dot or comma as the decimal separator.
Annulus Area Calculator
Result:
Annulus Area Formula
The area of an annulus is calculated by subtracting the area of the inner circle from the area of the outer circle:
A = π × (R² − r²)
Where R is the outer radius and r is the inner radius. It is required that R > r for the annulus to exist.
Practical Examples
| Outer Radius (R) | Inner Radius (r) | Area (A = π × (R² − r²)) |
|---|---|---|
| 8 m | 5 m | 122.522 m² |
| 10 cm | 6 cm | 201.062 cm² |
| 7 m | 3 m | 125.664 m² |
| 5 cm | 2 cm | 65.973 cm² |
| 12 m | 8 m | 251.327 m² |
Frequently Asked Questions
What is the formula for the area of an annulus?
The area is A = π × (R² − r²). Example: R = 8 m and r = 5 m → A = π × (64 − 25) = π × 39 ≈ 122.522 m².
What is an annulus?
An annulus is the flat region bounded by two concentric circles (same center), one larger and one smaller. Visually, it looks like a ring or a flat washer.
What is the difference between an annulus and a circle?
A circle is a complete flat region, while an annulus is the difference between two concentric circles — that is, a larger circle with a circular “hole” in the center.
Can I use a comma instead of a decimal point?
Yes. This calculator accepts both a comma and a dot as the decimal separator.
See also…
