Maths & numbers
Annulus calculator
Find the area, ring width and boundary lengths of a circular ring.
A clear answer. Here’s how.
Requires 0 ≤ inner radius ≤ outer radius. Ring area = π(R−r)(R+r), width = R−r, and the two boundary lengths are 2πR and 2πr. Uses one consistent input length unit; area is in its square.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Outer radius
- 5
- Inner radius
- 3
Example result
- Ring area
- 50.2654824574
- Radial ring width
- 2
- Outer circumference
- 31.4159265359
- Inner circumference
- 18.8495559215
- Combined boundary length
- 50.2654824574