What Is Bending Stress?
When a beam bends under load, fibers on one side stretch (tension) and fibers on the other compress. Bending stress measures the intensity of that internal stress at a given point in the cross-section.
The Flexure Formula
The standard flexure formula is σ = M·c / I, where M is the bending moment, c is the distance from the neutral axis to the outermost (extreme) fiber, and I is the moment of inertia of the cross-section about the neutral axis. The result gives the maximum normal stress at the top or bottom of the beam.
This calculator is a quick reference for general planning and educational purposes. Comparing the computed stress against a material’s allowable stress is the basis of beam design, but real structural work should be verified by a licensed structural engineer using the applicable design code.