When to use this calculator
A washer, circular border or ring-shaped garden bed has the area of the outer circle minus the central opening.
Explore the circle & ellipse calculators for other questions in this topic. For a related calculation, use the Arc Length Calculator: Find the length of a circular arc from radius and central angle.
PUTTING IT INTO PRACTICE
Annulus Area: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Outer radius | 5 |
| Inner radius | 3 |
| Result | 50.265482 square units |
- Check the input labels and enter the example values above.
- Apply the relationship: Area = π(outer radius² − inner radius²).
- The result is 50.265482 square units, rounded for display.
How to interpret your result
The inner radius cannot exceed the outer radius.
Distinguish radius from diameter before entering measurements. Arc length follows the curve, while chord length runs straight between endpoints. Ring-shaped areas subtract the inner circle from the outer one.
Frequently asked questions
How is chord length different from arc length?
A chord is a straight line between two points on the circle. An arc follows the circular boundary between those points.
When is the annulus area calculator useful?
A washer, circular border or ring-shaped garden bed has the area of the outer circle minus the central opening.
How do I use the annulus area calculator?
Enter outer radius, inner radius. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Area = π(outer radius² − inner radius²).
What should I check before using the result?
The inner radius cannot exceed the outer radius.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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