EngineeringFormulaStress (σ)
Stress is internal force per unit area within a material, resisting an applied load.
Normal stress (σ = F/A) acts perpendicular to a cross-section; shear stress (τ = V/A) acts parallel to it. In bending, stress varies across the cross-section and depends on the section's geometry through σ = Mc/I or the equivalent σ = M/S form using section modulus. Base SI unit is the pascal (Pa); engineering work commonly uses MPa, ksi, or psi.
A material's actual allowable working stress is set well below its yield point by a safety factor, not up against it - a real design intentionally never operates near the values in the table below, which represent the point where permanent deformation begins, not a safe operating target.
Use the Stress Calculator for direct axial load over area, and Bending Stress or Section Modulus when the load creates a bending moment. Mixing those cases is a common source of false confidence.
Typical Yield Stress by Material
| Material | MPa | ksi / psi |
|---|---|---|
| Structural steel (A36) | ~250 | ~36 ksi |
| Structural steel (A992) | ~345 | ~50 ksi |
| Aluminum 6061-T6 | ~276 | ~40 ksi |
| Concrete (compressive strength) | 20–40 | 2,900–5,800 psi |
Used In These Calculators
Frequently Asked Questions
Stress and pressure are both force per area - why different names?
They're dimensionally identical, but the context differs: pressure describes a fluid pushing on a surface from outside; stress describes internal resistance within a solid material carrying a load. Some engineering references do use the terms closer to interchangeably in certain contexts, but this site keeps them separate to match how each is actually used across its calculators.
What happens to a material once it passes its yield stress?
Below the yield point, a material returns to its original shape once the load is removed (elastic deformation). Past it, some deformation becomes permanent (plastic deformation) - the material won't fully spring back. Yield stress, not the material's ultimate (breaking) strength, is what most structural design margins are measured against.
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