Formula and input notes
Elastic bending stress = bending moment in lb-in ÷ section modulus in in³
| Input | Practical note |
|---|---|
| Bending moment | Enter the governing moment in lb-ft; the calculator converts it to lb-in before dividing by section modulus. |
| Section modulus | Enter section modulus about the axis of bending in cubic inches; the tool divides moment in lb-in by this value. |
Worked bending stress example
Bending Stress Calculator example: 1,200 lb-ft × 12 ÷ 20 in³ = 720 psi elastic bending stress about the axis represented by the entered section modulus.
Interpret the elastic bending stress
Use the psi result as an elastic flexural-stress calculation for the stated section axis and have the complete member checked under applicable design rules.
Capacity and stability checks outside M divided by S
Sign convention, biaxial bending, noncompact sections, lateral buckling, holes, stress concentrations, composite action, and load combinations are not represented.
Questions specific to this calculation
What is section modulus in the bending-stress formula?
Section modulus is a geometric property of the cross-section about the bending axis. Use the value for the actual shape and orientation; using the strong-axis value for weak-axis bending gives the wrong stress.
Does calculated bending stress prove that a member is adequate?
No. The result is elastic stress from M/S only. Capacity checks may also require material strength factors, stability, shear, deflection, local buckling, connections, and governing load combinations.