Torque to Power Calculator
Enter torque and rotational speed to get mechanical power in kW and hp, with the torque converted to lb·ft for imperial work.
Open calculatorLast updated: 2026-09-15
How the calculation works
- Power is torque times angular velocity: P = T × 2π × n/60, simplified to T × n / 9549 in SI units.
- The tool converts the same power to horsepower (1.341 hp per kW) and the torque to lb·ft.
Worked example
Interpreting the result
At constant torque, power rises linearly with speed; at constant power, torque falls as speed rises. This is why vehicles feel strong at low RPM (high torque) and electric motors deliver full torque from zero RPM. Compare against motor nameplates: rated power is continuous output, not peak.
Assumptions
- Steady rotation at the stated speed — no acceleration torque included.
- Shaft power at the coupling; drivetrain losses downstream are not considered.
Limitations
- Does not apply to linear motion (use P = F × v).
- Engine 'brake horsepower' measured at the crank differs from wheel power by drivetrain losses (10–15%).
Power (kW) by torque and speed
| Torque | 750 RPM | 1,000 RPM | 1,500 RPM | 3,000 RPM |
|---|---|---|---|---|
| 10 N·m | 0.79 | 1.05 | 1.57 | 3.14 |
| 25 N·m | 1.96 | 2.62 | 3.93 | 7.85 |
| 50 N·m | 3.93 | 5.24 | 7.85 | 15.71 |
| 100 N·m | 7.85 | 10.47 | 15.71 | 31.42 |
| 200 N·m | 15.71 | 20.94 | 31.42 | 62.83 |
Power (kW) = torque (N·m) × speed (RPM) × 2π ÷ 60,000.
Worked scenario: 50 N·m at 1,500 RPM
The shaft power is 7.85 kW, or 10.5 hp. Doubling the speed at the same torque doubles the power, which is why a motor rated at 1,500 RPM and one at 3,000 RPM of equal torque differ so much in size and cost.
Mistakes to avoid
- Reading power as shaft power at the load without allowing for drive losses between motor and machine.
- Mixing lb·ft and N·m. One lb·ft is about 1.356 N·m.
- Using the rated speed when the machine runs slower under load.
Frequently asked questions
How many kW is 100 N·m at 3000 RPM?
100 × 3000 / 9549 = 31.4 kW, about 42 hp. The constant 9549 is 60,000/2π — it converts torque × angular velocity into kilowatts directly.
What's the difference between kW and hp?
They measure the same thing. 1 kW = 1.341 mechanical hp. Europe rates motors in kW; the US traditionally uses hp.