Enter outer diameter and inner diameter, then click Calculate to get annulus area and ring diameter difference.
Both outputs are shown here for quick reading.
D is the outer diameter and d is the inner diameter. Square both, subtract, multiply by π, then divide by 4 to get annulus area.
On this page, ring diameter difference is defined as D - d for quick dimension checks.
Outer diameter must be larger than inner diameter.
Keep units consistent, such as all in mm, cm, or m.
Results trim unnecessary trailing zeros for easier copy use.
An annulus is the region between two concentric circles. It appears in many parts such as washers, flanges, and ring-shaped components. To find annulus area, subtract inner circle area from outer circle area.
This calculator takes outer and inner diameter and returns two outputs at the same time: annulus area and ring diameter difference (outer minus inner).
In engineering and manufacturing, annulus area is often used for material estimation, section analysis, and drawing verification. Online calculation helps avoid manual mistakes.
Always ensure outer diameter is greater than inner diameter and keep units consistent for correct results.
Use A = π × (D² - d²) / 4.
Yes, decimal values are supported.
Because otherwise the annulus is not geometrically valid.
It is outer diameter minus inner diameter, D - d.
It is the square of your input unit, such as mm² or cm².
Students, teachers, engineers, and anyone doing geometry calculations.
Yes, it is fully usable on mobile browsers.
To avoid accidental editing and keep outputs easy to copy.
This page requires values greater than 0 for consistent input rules.
Yes, gasket and ring component estimates are common use cases.
Useful for gasket area estimates, cross-section checks, and geometry study.
Scan the QR code to use this tool on mobile.