Enter the total kVA, horsepower, and voltage into the calculator to determine the locked rotor amps.

Locked Rotor Amps Formula

The following formula is used to calculate locked rotor amps.

LRA = 1000*(kVA/HP)/V
  • Where LRA is the locked rotor amps
  • kVA is the kilovolt-amps
  • HP is the horsepower
  • V is the voltage

To calculate the locked rotor amps, divide the kVA by the horsepower, multiply that result by 1000, then divide the result by the voltage.

What is locked rotor amps?


Locked rotor amps are defined as the inrush current received by a motor or generator.

How to calculate locked rotor amps?

Example Problem:

The following example outlines how to calculate locked rotor amps.

First, determine the kVA of the system. In this example, the starting kVA is 500.

Next, determine the horsepower of the engine. In this problem, the engine has a horsepower of 100.

Next, determine the voltage of the motor. This motor receives a voltage of 120V.

Finally, calculate the locked rotor amps using the formula above:

LRA = 1000*(kVA/HP)/V

LRA = 1000*(500/100)/120

LRA = 41.666 amps