Annulus Calculator (A = π(R²−r²))

The calculator applies the exact formula A = π(R² − r²), w = R − r. Worked example: R = 8 cm, r = 5 cm → A = 122.52 cm², w = 3 cm. Keep every input in one unit system and the result follows in square units (m², ft², cm²); full precision is kept until the final rounding. All side lengths must share one unit or the area comes out scaled wrongly.

1. 1

   Enter the measurements

   Type the values required by the formula for annulus properties.

2. 2

   Check the units

   One unit system throughout — cm, m, ft or in.

3. 3

   Read the result

   The calculator substitutes, evaluates and rounds only at the end.

• 1

  Area scales with the square of linear dimensions

• 2

  1 m² = 10.764 ft² for quick conversion

• 3

  Sketch and label the shape before entering values

• Unit mix-ups between cm² and m² (factor 10,000)

• Using a slanted length as a perpendicular height

• Treating an irregular shape as regular