Shaft Torque Calculator
Calculate shaft torque from power and speed, or power from torque and speed.
torque
power
shaft
motor
Nm
kW
RPM
coupling
Input values
⚙
Enter values and click Calculate to see results here.
Formula
T = (P × 60) / (2π × N) [Nm]
P = (T × 2π × N) / 60 [W]
Worked Example
Given: A 5.5 kW motor runs at 1450 RPM.
Step 1: T = (5500 × 60) / (2π × 1450) = 330,000 / 9110.6 = 36.2 Nm
Verify: P = (36.2 × 2π × 1450) / 60 = 5497 W ≈ 5.5 kW ✓
The shaft coupling must be rated for at least 36.2 Nm. Apply a service factor of 1.5 for shock loads.
Engineering Notes
- Service factor: For direct coupling to the load, use 1.0-1.25. For belt/gear drives with shock loads, use 1.5-2.0.
- Shaft diameter: The minimum shaft diameter for a given torque is d = (16T / πτ)^(1/3) where τ is the allowable shear stress.
- Coupling selection: Always select a coupling rated for higher torque than the calculated value. Misalignment reduces coupling life.
- Peak torque: During acceleration, torque can be 2-3× the running torque. Size the shaft and coupling for peak torque.
References
- IEC 60034-1 — Rotating electrical machines