Shaft Torsional Stress Calculator
Find the maximum torsional shear stress in a solid round shaft from transmitted torque and shaft diameter, with an optional factor-of-safety check against an allowable stress.
Enter your values
Torque and shaft diameter, plus an optional allowable stress.
How this calculator works
For a solid round shaft in pure torsion, the maximum shear stress occurs at the outer surface:
T is the transmitted torque and d is the shaft diameter. If you provide an allowable shear stress for the shaft material, the calculator also reports the resulting factor of safety, FS = allowable ÷ calculated stress.
Typical allowable shear stress by material
| Material | Allowable shear (MPa) |
|---|---|
| Mild steel (AISI 1018) | ~40 – 50 |
| Medium carbon steel (AISI 1045) | ~55 – 70 |
| Alloy steel (AISI 4140, Q&T) | ~90 – 130 |
These are rough estimation values — always check the actual shaft material's yield or endurance shear strength and apply the design code's own safety factor.
Frequently asked questions
Does this account for bending or fatigue?
No — this is a pure torsion check. Shafts carrying bending loads or fluctuating torque should also be checked with a combined-stress and fatigue approach, such as the ASME shaft design equation.
How is this different from the Shaft Diameter Calculator?
The Shaft Diameter Calculator sizes a shaft from a target stress; this calculator checks the stress in a shaft whose diameter is already fixed.