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How to Calculate Motor Speed

Updated March 22, 2017

Many car enthusiasts want to know the exact motor speed of their car but do not know how to calculate this number. In reality, the equation for calculating motor speed is very simple and straightforward. In addition, this formula can be applied to a variety of motors and does not work only for automobile motors specifically. As a result, this formula can be used to determine the motor speed for almost any motor and only requires investigating the measurement of the power source that the motor is connected to.

Look up the frequency for the power supply to the motor. This number should be indicated on the power supply itself, or you can contact your local electronics store to ask how to find out the power supply frequency.

Multiply the supply frequency by 120. The number 120 is a constant when calculating motor speed, and thus never changes.

Divide the resulting number by the number of winding poles in the motor. The end result is the motor speed of the motor, measured in Srpm, or synchronous revolutions per minute.

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About the Author

James Wiley graduated from Providence College in 2009 as a double major in global studies and Spanish. Wiley's capstone thesis paper was published in the Providence College database. He has also competed in international script-writing competitions and coauthored a pilot which placed in the top 15 percent of international entries over the past year.