Home › Geometry › Annulus Calculator
Annulus Calculator
Enter outer and inner radius — ring area and circumferences update instantly.
Formula
Area = π(R²−r²) = π/4·(OD²−ID²)
Example
OD 100 mm, ID 80 mm pipe bore → Area = π/4·(100²−80²) = 2827 mm².
FAQ
How do I use diameters instead of radii?
Area = π/4 × (OD² − ID²). The OD/ID form is the standard one for pipe bores and gaskets.
What is the area of a pipe cross-section wall?
Exactly the annulus area between OD and ID — used for flow area and material weight estimates.