Online Tool Store
Shaft Diameter Calculator
Shaft Diameter Calculator handles combined torsion and bending; fatigue and the keyway are what a real design has to add.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Math & Science
Shaft Diameter Calculator
Frontend preview — no upload or external service.
Minimum diameter
15 kW at 1450 rpm is 98.8 Nm of torque. Combined with 85 Nm of bending at 40 MPa allowable shear, the minimum diameter is about 27 mm before any keyway allowance.
How the Shaft Diameter Calculator works
- Enter the transmitted power and speed, which give the torque.
- Add the bending moment from the shaft's loading and supports.
- Add allowances for keyways, stress concentrations and fatigue, then treat the result as preliminary and have it reviewed.
The method
Torque follows from power and speed, and the combined loading determines the required section modulus.
T = 9550 x kW / rpm, then d = cube root of (16 x sqrt(M^2 + T^2) / (pi x tau))
A keyway removes material and concentrates stress, commonly requiring several percent of extra diameter beyond the calculated figure.
FAQ
Why does a keyway matter?
Because it removes material and concentrates stress at a sharp corner. A shaft sized to the calculated diameter and then cut with a keyway is undersized, and the corner is where fatigue cracks start.
Is static calculation enough?
No. A rotating shaft under bending experiences fully reversed stress every revolution, which is a fatigue problem rather than a static one. Fatigue analysis governs most real shaft failures.
Can I use this for a real design?
As a preliminary check only. Real shaft design covers fatigue, stress concentrations, deflection, critical speed and bearing loads, and it needs a qualified engineer.
How we compare
| Feature | Online Tool Store | A graphing calculator | A stats package |
|---|---|---|---|
| Combined loading | ✓ | Torque only | ✓ |
| Explains keyway allowance | ✓ | ✗ | ✗ |
| No sign-up | ✓ | ✓ | ✗ |
| Nothing uploaded | ✓ | ✗ | ✗ |
Shaft Diameter Calculator handles combined torsion and bending; fatigue and the keyway are what a real design has to add.