Output Torque Calculator
Calculate output torque from power and speed, or through a gear reduction.
Output torque is the twisting force at a shaft's output, after any gear reduction. This calculator finds it from power and output speed — essential for sizing gearmotors, winches, and drive systems.
Output Torque Formula
Gear reduction trades speed for torque: halving the output speed roughly doubles the torque for the same power. That's why winches and industrial gearmotors run at low output RPM to produce huge torque.
How to Use This Calculator
- Enter power in horsepower.
- Enter output speed in RPM (after any gearbox).
- Read output torque in lb-ft and Nm.
Worked Example
How Gear Reduction Multiplies Torque
A gearbox trades rotational speed for torque while keeping power (minus small losses) roughly constant. Cut the output speed in half through a 2:1 reduction and the output torque nearly doubles. This inverse relationship is why the formula divides by output RPM — the slower the final shaft turns, the more torque it delivers. Winches, hoists, conveyors, and industrial gearmotors all exploit this to turn modest motor power into enormous low-speed force.
Sizing a Gearmotor or Drive
To pick a gearmotor, start from the torque your load actually needs at its operating speed, then work back to required power. Always allow a service-factor margin for starting torque and shock loads, which can briefly exceed running torque several times over. Output torque in lb-ft converts to Nm by multiplying by 1.3558.
Output Torque for 10 HP by Speed
| Output RPM | Torque (lb-ft) | Torque (Nm) |
|---|---|---|
| 50 | 1,050 | 1,424 |
| 100 | 525 | 712 |
| 250 | 210 | 285 |
| 500 | 105 | 142 |
Frequently Asked Questions
Use Torque (lb-ft) = (HP × 5252) ÷ output RPM. The output RPM is the speed after any gear reduction.
Gear reduction increases torque in proportion to the reduction ratio. A 10:1 reduction multiplies torque by about 10 (minus gearbox losses) while dividing speed by 10.
Because for a fixed power, torque and speed trade off inversely. Lower output speed concentrates the same power into more twisting force.
Multiply pound-feet by 1.3558 to get newton-metres.
No — it gives the ideal output torque. Multiply by the gearbox efficiency (often 0.9–0.98) for the real delivered torque.