Shaft Power Calculator
Find mechanical power from torque and RPM.
Results update as you type.
How it works
Shaft power is the mechanical power transmitted by a rotating shaft, and this shaft power calculator finds it in watts from the torque on the shaft and its rotational speed in RPM. Power combines how hard the shaft twists with how fast it spins, giving the rate at which it does useful work, which is the true measure of what a motor, engine, or turbine can deliver to a load. This matters when specifying and matching rotating machinery: pumps, fans, compressors, gearboxes, and generators are all rated by power because it determines how much work they move per second. Torque or speed on its own can mislead, since a shaft with high torque but low speed may deliver little power. A shaft power calculator gives the combined figure directly in SI watts for clean comparison and sizing. The formula works because power equals torque times angular velocity, and angular velocity in radians per second comes from the RPM multiplied by two pi and divided by sixty. This converts revolutions per minute into the radians per second that pair correctly with torque in newton-metres to yield watts. Mechanical engineers, technicians, and students use a shaft power calculator to relate torque, speed, and power across drivetrains and rotating equipment.
P = torque × 2π × rpm ÷ 60
Mechanical power on a rotating shaft equals torque times angular velocity. Angular velocity in radians per second is the rotational speed in revolutions per minute multiplied by two pi, because each revolution is two pi radians, and divided by sixty to convert minutes to seconds. Multiplying torque by this angular velocity gives power directly in watts, tying the twisting force and the turning rate into a single measure of work done per second.
Source:Standard mechanical engineering (rotational power)
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
Shaft power updates instantly as you type — no button to press.
Frequently asked questions
How is shaft power calculated from torque and RPM?
Shaft power equals torque multiplied by angular velocity. Convert the rotational speed from RPM to radians per second by multiplying by two pi and dividing by sixty, then multiply by the torque in newton-metres to get power in watts. For example, 50 newton-metres at 3000 RPM gives about 15708 watts. This directly combines the twisting force and turning speed into a single power figure.
Why multiply RPM by 2π and divide by 60?
Torque times angular velocity gives power only when angular velocity is in radians per second. Each revolution is two pi radians, so multiplying RPM by two pi converts revolutions to radians, and dividing by sixty converts per minute to per second. The combined factor turns a familiar RPM figure into the radians-per-second value that pairs correctly with newton-metres of torque to produce watts.
What is the difference between torque and power?
Torque is the twisting force the shaft applies at any instant, while power is the rate at which that force does work as the shaft turns. A slow shaft with high torque can deliver the same power as a fast shaft with low torque. Power, which folds in the speed, is what ultimately determines how quickly a machine can move its load.
How do I convert the result to horsepower or kilowatts?
This calculator gives power in watts. Divide by 1000 to get kilowatts, the standard metric rating for motors. To convert to mechanical horsepower, divide the watts by about 745.7. So 15708 watts is roughly 15.7 kilowatts or about 21 horsepower. Choose whichever unit matches the nameplate or specification you are comparing against for your equipment.
Does this give input or output power?
It gives the mechanical power at the shaft corresponding to the torque and speed you enter. Whether that is input or output power depends on where you measure. Real machines lose some power to friction, windage, and heat, so the electrical input to a motor exceeds its shaft output. Divide shaft power by efficiency to estimate input power, or multiply input by efficiency for output.