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structural / geometry

Circular section properties calculator.

Calculate gross area, centroidal second moment of area, elastic section modulus, and radius of gyration for a solid circular section.

read the result

A circle has one centroidal diameter property set.

For a solid circle, every centroidal diameter has the same geometric properties. The diameter controls area, stiffness-related second moment, elastic section modulus, and radius of gyration.

Governing equations

For outside diameter D: A = πD2/4, I = πD4/64, Z = πD3/32, and r = √(I/A) = D/4.

The calculator evaluates the equations in millimetres, then reports area in cm2, second moment in cm4, section modulus in cm3, and radius in mm.

Use gross properties carefully.

  • Openings, voids, hollow walls, reinforcement, cracking, composite action, and effective properties are not included.
  • The reported I and Z values are about a centroidal diameter; no weak-axis distinction exists for a perfect solid circle.
  • Carry the properties into a separate stress, buckling, deflection, or code-resistance check with consistent units.