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.
Last 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.
Formula
P(kW) = T(N·m) × RPM / 9549 hp = kW × 1.341
| Symbol | Meaning | Unit |
|---|---|---|
P | Mechanical power | kW |
T | Torque | N·m |
n | Rotational speed | RPM |
Worked example
A motor delivering 50 N·m at 1500 RPM produces 50 × 1500 / 9549 = 7.85 kW ≈ 10.5 hp — right at the rating of a common 7.5 kW motor at service factor.
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%).
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.