Annulus Calculator
Calculate the area of a ring-shaped annulus.
How to Use the Annulus Calculator
Enter the outer and inner radii to calculate the area of the ring-shaped region between two concentric circles.
Practical Example
With outer radius 6 and inner radius 4, the annulus area is about 62.83 square units.
Factors That Affect the Result
The inner radius must be smaller than the outer radius, and both measurements must use the same unit.
Frequently Asked Questions
What is an annulus?
It is the region between two concentric circles.
Can the radii be equal?
If they are equal, the annulus area is zero.
How is area calculated?
Use π times the difference between the squared radii.
Related Tools
- Circle Calculator
- Sector Area Calculator
- Circle Segment Calculator
- Chord Length Calculator
- Area Calculator
Working with Annulus Measurements
An annulus is the ring-shaped region between two concentric circles. Its area is found with π(R² − r²), where R is the outer radius and r is the inner radius. The outer radius must be greater than the inner radius, and both values must use the same unit.
This calculation is useful for washers, gaskets, circular tracks and ring-shaped surfaces. If you are measuring diameters instead of radii, divide each diameter by two before applying the formula. Small measurement errors can have a noticeable effect because both radii are squared, so use consistent and reasonably precise dimensions when the result feeds into material or manufacturing estimates.