Electric Motor Torque Calculator
Torque is the rotational force a motor delivers to its shaft, and it is directly tied to mechanical power and rotational speed. For any rotating machine the relationship is simple: torque equals power divided by angular speed. This calculator takes the mechanical output power and the shaft speed in revolutions per minute and returns torque in newton-metres, the same torque expressed in pound-feet, the angular speed in radians per second, and the equivalent power in horsepower. Use it to size couplings, check gear ratios, or confirm a motor nameplate.
Motor torque formula
Angular speed omega = 2 * pi * RPM / 60 (rad/s)
Torque T = Power / omega (N.m)
Shortcut: T = 9.5493 * Power(W) / RPM
Torque (lbf.ft) = T * 0.737562
Power (hp) = Power(W) / 745.699872
The conversion factors are exact: 1 N.m = 0.737562 lbf.ft and 1 mechanical horsepower = 745.699872 watts. Enter mechanical shaft power for shaft torque.
Torque and motor sizing context
- For constant power, torque rises as speed falls, which is why reduction gearing multiplies torque.
- Use mechanical output power, not electrical input. Input power times efficiency gives output power.
- Standard US induction motors run near 1,750 or 3,500 RPM at 60 Hz under load (4-pole and 2-pole).
- Newton-metres and pound-feet are interchangeable through the exact 0.737562 factor.
- Starting (locked-rotor) torque can be several times rated torque; this tool computes rated continuous torque.
Motor torque: frequently asked questions
What is the formula for motor torque from power and speed?
Torque equals power divided by angular speed. With power P in watts and speed n in revolutions per minute, torque T in newton-metres is T = P times 60 divided by (2 times pi times n), which simplifies to T = 9.5493 times P / n. Angular speed in radians per second is omega = 2 times pi times n / 60.
How do I convert between newton-metres and foot-pounds of torque?
One newton-metre equals 0.737562 pound-feet (lbf.ft), and one pound-foot equals 1.355818 newton-metres. These come from the defined values of the pound-force, the foot, and the newton, so the conversion is exact to the digits shown.
How is horsepower related to power in watts?
One mechanical (imperial) horsepower equals 745.699872 watts by definition. So a motor rated at 1,000 watts of mechanical output produces about 1.341 horsepower. Electrical input power will be higher than mechanical output because of motor losses.
Is this the electrical input or mechanical output torque?
Enter the mechanical (shaft) output power to get shaft torque. If you only know electrical input power, multiply it by the motor efficiency (a value you supply) to estimate shaft power first. This calculator works on whatever power figure you enter, so use the mechanical output for shaft torque.
Why does torque rise as speed falls for a fixed power?
Because torque is power divided by speed. For a constant power output, halving the rotational speed doubles the torque. This is why gearboxes that reduce speed increase available torque, ignoring losses, and why motors deliver high torque near stall.
Official sources
- NIST: CODATA fundamental constants and SI units.
- NIST: Office of Weights and Measures (unit definitions).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.