Annulus Calculator
Math
Calculate the area between two concentric circles.
Formula
A = π(R² − r²)
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
Example Calculation
Example inputs
- Outer radius: 5
- Inner radius: 3
Radii 5 and 3 enclose an annulus of area 16π.
Frequently asked questions
How do I use this calculator?
Enter outer radius, inner radius. The result updates automatically. Use Reset to restore the example values.
What method does it use?
A = π(R² − r²). Follow the units and definitions shown with the inputs to apply this relationship consistently.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.