Work out bending stress in beam instantly with clear inputs, formula shown and shareable results.
Bending stress is moment divided by section modulus, sigma = M / Z. Keeping units consistent, a moment in kilonewton metres becomes newton millimetres by multiplying by a million, and a modulus in cubic centimetres becomes cubic millimetres by multiplying by a thousand. Allowable stress in working stress design is conventionally 0.66 times yield.
Bending stress
sigma = M / Z
Capacity
M capacity = 0.66 x fy x Z
Preliminary estimate only. Member design must be verified by a qualified structural engineer including lateral torsional buckling, shear and deflection checks.
sigma = M / Z. Bending stress is moment divided by section modulus, sigma = M / Z.
In limit state design, where the section is compact enough to develop a full plastic hinge. The plastic modulus is typically 10-20 percent larger than the elastic value for a rolled I section.
This calculator takes 3 inputs: Applied bending moment, Elastic section modulus, Steel yield strength. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.