Motor Power Calculator
Convert torque and RPM to horsepower and kW.
Shaft torque in pound-feet.
Results update as you type.
How it works
Motor power tells you how much work a rotating machine can do each second, and this motor power calculator converts a torque and a rotational speed into power expressed in both horsepower and kilowatts. Torque is the twisting force on the shaft and RPM is how fast it spins; power combines the two, because a motor that produces high torque at high speed delivers more usable output than one that manages only one of those. This matters when selecting or comparing motors and engines: fans, pumps, conveyors, vehicles, and machine tools are all specified by power because it sets how quickly they can move a load. Torque alone or speed alone can mislead, so a motor power calculator gives the single figure that captures true capability, letting you match a motor to the job without over- or under-sizing it. The formula works because power equals torque multiplied by rotational speed, and the constant 5252 converts pound-feet and RPM into horsepower cleanly. Multiplying by 0.7457 then restates that figure in kilowatts for metric specifications. Automotive engineers, machine designers, and technicians rely on a motor power calculator to read across between torque curves and power ratings and to compare drives on equal terms.
hp = torque × rpm ÷ 5252
Mechanical power is torque times rotational speed. Using pound-feet and revolutions per minute, the constant 5252 converts the product into horsepower, because one horsepower is 33,000 pound-feet per minute and dividing that by two pi radians per revolution yields 5252. Multiplying the horsepower result by 0.7457 converts it to kilowatts, since one horsepower equals 745.7 watts by definition.
Source:Standard 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 torque and rotational speed.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Power updates instantly as you type — no button to press.
Frequently asked questions
How is horsepower calculated from torque and RPM?
Horsepower equals torque in pound-feet multiplied by rotational speed in RPM, divided by the constant 5252. This constant arises because one horsepower is defined as 33,000 pound-feet of work per minute, and dividing by two pi converts the rotation into that unit. The formula shows that power depends on both how much twisting force a shaft produces and how fast it turns.
Why is the constant 5252 used?
The number 5252 comes from the definition of horsepower as 33,000 pound-feet per minute divided by two pi radians in one revolution, which gives roughly 5252. It ties together the customary units of torque in pound-feet and speed in revolutions per minute. Because of this constant, torque and horsepower curves for any engine always cross at exactly 5252 RPM when plotted together.
What is the difference between torque and power?
Torque is the instantaneous twisting force a shaft can apply, while power is the rate at which that force does work over time. A motor can have high torque but low power if it turns slowly, or high power from modest torque if it spins fast. Power, combining both, determines how quickly a load can be moved, which is why it is the headline rating for most machines.
How do I convert horsepower to kilowatts?
Multiply horsepower by 0.7457 to get kilowatts, because one horsepower equals 745.7 watts by definition. This calculator performs the conversion automatically, showing both units side by side. Kilowatts are the standard metric unit for motor power and appear on most electric motor nameplates worldwide, while horsepower remains common for engines and equipment specified in the United States and older machinery.
Does this work for electric motors and engines alike?
Yes. The relationship between torque, speed, and power is the same for any rotating shaft, whether driven by an electric motor, a petrol engine, or a turbine. As long as you supply the shaft torque in pound-feet and the speed in RPM, the calculated power applies. Note that electric motors often quote a continuous rating, while engines quote a peak figure at a specific speed.