Bending Stress Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter the bending moment M in kN·m (from a beam calculator).
- Enter the section modulus Z in cm³ — or, if you don't have Z, enter the second moment of area I and the distance to the extreme fibre c instead.
- Read the peak bending stress in MPa.
How it works
The Bending Stress Calculator gives the peak fibre stress in a bent member from σ = M / Z, where Z is the section modulus.
If you only have the second moment of area I and the distance from the neutral axis to the outer fibre c, it uses the equivalent form σ = M·c / I (because Z = I / c). The largest stress is at the fibre furthest from the neutral axis.
Worked example
22.5 kN·m on Z = 667 cm³. σ = 22.5×10⁶ N·mm ÷ 667,000 mm³ ≈ 33.7 MPa — comfortably below the ~250 MPa yield of mild steel.
Tips
- Get M from the Simply Supported or Cantilever Beam Calculator and Z from the Section Modulus Calculator.
- Keep units consistent — kN·m in gives MPa out here automatically.
Frequently asked questions
Is this the maximum stress in the beam?
It's the maximum bending stress for the moment you enter. Real members can also carry shear, axial and bearing stresses, and stress concentrations at holes or notches — check those separately.
Can I use these results for final design?
No. These calculators are for first-pass sizing, checking and learning. They assume ideal supports, static loads and elastic behaviour, and they don't apply load factors, member capacity, buckling or connection checks. Always verify against the relevant design code (e.g. AS 4100, AS 1170, Eurocode) and have a qualified engineer sign off structural work.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.