Power Transmission Calculator
Power, Torque, and Speed Are Never Independent
Any rotating shaft ties together three quantities that can't be chosen separately: the power it transmits, the torque it carries, and the speed it spins at. Fix any two and the third is determined. This calculator moves in both directions — finding power from a known torque and speed, or the torque needed to deliver a known power at a given speed.
The Formulas
T = P / ω
ω is angular velocity in radians per second, converted from rotational speed N in rpm. Power comes out in watts and is also expressed in kilowatts and horsepower for convenience.
Worked Examples
| Direction | Inputs | Result |
|---|---|---|
| Power from Torque | 150 N·m at 1,800 rpm | 28.2743 kW (37.9165 hp) |
| Power from Torque | 50 N·m at 3,000 rpm | 15.708 kW (21.0647 hp) |
| Torque from Power | 75 kW at 1,800 rpm | 397.8874 N·m |
At a fixed power level, torque and speed are inversely related — the same 75 kW delivered at double the rpm would require roughly half the torque.
Where This Calculation Matters
- Motor selection — confirming a motor's rated power is sufficient to deliver the torque a load needs at its operating speed.
- Coupling and shaft sizing — converting a power rating into the torque value needed to size downstream components.
- Gearbox specification — checking that torque and speed at each stage of a reduction stay within component ratings.
How to Use This Calculator
- Choose the direction: Power from Torque or Torque from Power.
- For power from torque, enter Torque (N.m) and Rotational Speed (RPM).
- For torque from power, enter Power (kW) and Rotational Speed (RPM).
- Select Calculate to get the corresponding result.
Related Calculations
Feed the resulting torque directly into the Shaft Diameter Calculator to size the shaft carrying it, or into the Gear Design Calculator if it's entering a gear train.