Motor Torque, Power and RPM Calculator

Find shaft torque from power and speed, or the power needed for a given torque, for motor and gearbox sizing.

Torque
Power in HP
Torque in lb·ft

Runs entirely in your browser. Nothing you enter is sent anywhere.

How it works

Mechanical power is torque times angular speed. With power in watts and speed in revolutions per minute, torque in newton-metres is power × 60 / (2π × RPM), often written with the constant 9549 when power is in kilowatts.

Use the motor's rated values from its nameplate. Through a gearbox, torque rises and speed falls by the gear ratio, minus the gearbox's efficiency losses.

T (N·m) = 9549 × P (kW) / n (rpm)
P (kW) = T × n / 9549
1 HP = 0.7457 kW

Worked example

A 7.5 kW four-pole motor running at 1,440 rpm delivers 9549 × 7.5 / 1440 = 49.7 N·m. Through a 10:1 gearbox at 95% efficiency that becomes about 472 N·m at 144 rpm.

Frequently asked questions

Why is the constant 9549?

It's 60,000 / 2π, which converts kilowatts and revolutions per minute into newton-metres in one step.

Does a motor deliver rated torque at all speeds?

No. An induction motor on a fixed supply runs near its rated speed. On a VFD, torque is roughly constant up to base speed, then falls as speed rises further (constant-power region).

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