Motor Torque Calculator
Find motor torque from power and speed.
Results update as you type.
How it works
Motors are rated by power, but torque is what turns the load, and this calculator converts between them. You enter the motor's power in kilowatts and its speed in RPM, and it returns the torque in newton-meters and pound-feet. The relationship comes from the fact that power equals torque times rotational speed; rearranged into practical units, torque in newton-meters equals power in kilowatts times 9549.3 divided by RPM. The constant folds in the conversion from kilowatts and RPM to newton-meters. A key insight is the inverse relationship between torque and speed at constant power: a motor running slowly produces high torque, while the same motor at high speed produces low torque. This is why gear reductions are used to trade a motor's high speed for the greater torque a load needs, and why low-speed applications require either large motors or gearing. This calculation is essential for selecting motors and drives, sizing gearboxes, and verifying that a motor can deliver the torque a machine demands at its operating speed. It applies to electric motors, engines, and any rotating power source. The result assumes the power and speed are at the same operating point. For horsepower, note that torque in pound-feet also equals 5252 times horsepower divided by RPM, an equivalent relationship. Enter the power and speed to find the motor torque.
T (N·m) = P (kW) × 9549.3 / RPM
Torque relates to power and rotational speed: power equals torque times angular velocity. Rearranged for common units, torque in newton-meters equals the power in kilowatts times 9549.3 divided by the speed in RPM. At a given power, lower speed means higher torque.
Source:Electrical / mechanical engineering
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter motor power and speed.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Torque updates instantly as you type — no button to press.
Frequently asked questions
How do you calculate motor torque from power?
Torque in newton-meters equals the power in kilowatts times 9549.3 divided by the speed in RPM. For a 15 kW motor at 1500 RPM, that is about 95.5 newton-meters. The calculator also converts to pound-feet. This comes from the fundamental relationship that power equals torque times rotational speed.
Why does torque decrease as speed increases?
For a fixed power, torque and speed are inversely related because power equals torque times angular velocity. So a motor producing a given power delivers high torque at low speed and low torque at high speed. This trade-off is why gear reductions convert a motor's high speed into the higher torque many loads require.
What is the constant 9549.3?
The constant 9549.3 combines the unit conversions needed to get torque in newton-meters directly from power in kilowatts and speed in RPM. It comes from 60 seconds per minute divided by 2 pi (to convert RPM to radians per second) times 1000 (kilowatts to watts). Using it avoids manual unit conversions.
How is this related to horsepower and 5252?
In imperial units, torque in pound-feet equals 5252 times horsepower divided by RPM, the same physical relationship in different units. The number 5252 is where a torque and horsepower curve always cross on a dynamometer chart. This calculator works in kW and newton-meters but also provides pound-feet for convenience.
How is motor torque used in design?
Engineers use it to select motors and gearboxes that can supply the torque a machine needs at its operating speed. If a load requires more torque than the motor provides at the required speed, a gear reduction increases torque at the cost of speed. Verifying torque at the operating point ensures the drive can move the load.