Torsional Constant Calculator

Find the polar moment / torsional constant of a solid round shaft.

Torsional constant J (mm⁴) 251,327.41

Formula: J = π·d⁴ ÷ 32

Step-by-step with your numbers:

1. Values used:

2. Diameter = 40

4. Torsional constant J = 251,327.41mm⁴

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The torsional constant (polar moment of inertia) measures a shaft's resistance to twisting.

The math behind it

For a solid circular shaft, J = π·d⁴ ÷ 32. The fourth-power dependence makes diameter dominant.

40 mm shaft → J ≈ 251,327 mm⁴.

Why d⁴?

Material far from the axis resists twisting much more strongly.