Shaft Diameter Calculator

Inputs

Torque (T)

Torque carried by the shaft.

N·m

Bending moment (M)

Optional bending moment at the critical shaft section. Leave 0 for pure torsion.

N·m

Allowable shear stress (tau_allow)

Material allowable shear stress before applying the safety factor. If already derated, set safety factor to 1.

MPa

Safety factor (N)

Design stress is allowable shear stress divided by this factor.

Default result

Required diameter(d)

23.35mm

Pass

Round up to the next available stock diameter, then recheck stress and deflection.

Theoretical minimum solid round diameter. Round up to a stock size.

Also computed

Equivalent torque(T_e)100N·m

sqrt(T^2 + M^2) for the maximum-shear combined-load formula.

Max shear at diameter(tau_max)40MPa

Equals the design shear stress at the solved diameter.

Design shear stress(tau_d)40MPa

allowable shear / safety factor.

Torsional shear(tau_t)40MPa

Bending stress(sigma_b)0MPa

Polar moment J(J)2.919cm⁴

J = pi d^4 / 32 for a solid round shaft.

Method notes 3 notes

Pure torsion uses tau = 16T/(pi d^3). With bending included, the maximum-shear check is tau_max = sqrt((sigma_b/2)^2 + tau_t^2).
The combined-load rearrangement is d = [16*sqrt(T^2 + M^2)/(pi*tau_d)]^(1/3), with T and M in N*mm and tau_d = tau_allow / safety factor.
This is a static solid-shaft screen. It does not include fatigue, stress concentrations at keyways/shoulders, shaft deflection, critical speed, material yield in bending, or bearing reactions.