Math
Circle
Calculate area, circumference, and diameter.
Calculators / Math / Annulus area
Annulus area calculator
Find the area of a circular ring by subtracting the inner disk from the outer disk, and add both circumferences for its total boundary.
On this page
Area50.27units²
Boundary length50.27units
Calculator controls
How to calculate
Find the area of a circular ring by subtracting the inner disk from the outer disk, and add both circumferences for its total boundary.
Area = pi*(R^2-r^2) units²; Boundary length = 2*pi*(R+r) units
Worked example
Outer radius: 5; Inner radius: 3.
Area: 50.27 units²; Boundary length: 50.27 units.
Assumptions and limits
Find the area of a circular ring by subtracting the inner disk from the outer disk, and add both circumferences for its total boundary. Use the same length unit throughout. Angles marked degrees use degrees. Results describe ideal geometric shapes.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Find the area of a circular ring by subtracting the inner disk from the outer disk, and add both circumferences for its total boundary.
When this tool is useful
Area = pi*(R^2-r^2) units²; Boundary length = 2*pi*(R+r) units
Understanding your inputs
| Input | What to enter |
|---|---|
| Outer radius | Enter a number of at least 1e-12 and no more than 1000000000000. |
| Inner radius | Enter a number of at least 0 and no more than 1000000000000. |
Frequently asked questions
What assumptions does this calculation use?
Find the area of a circular ring by subtracting the inner disk from the outer disk, and add both circumferences for its total boundary. Use the same length unit throughout. Angles marked degrees use degrees. Results describe ideal geometric shapes.
How is the result calculated?
Area = pi*(R^2-r^2) units²; Boundary length = 2*pi*(R+r) units