Enter the voltage, armature resistance, and the back e.m.f., into the calculator to determine the armature current.

Armature Current Formula

The following equation is used to calculate the Armature Current.

Ia = (V-E) / Ra
  • Where Ia is the armature current (amps)
  • V is the voltage from the source (volts)
  • E is the back e.m.f (volts)
  • Ra is the armature resistance (ohms)

To calculate the armature current, subtract the back e.m.f. from the source voltage, then divide by the armature resistance.

What is an Armature Current?


An armature current is defined as the total amperage moving through a system with a given voltage, emf, and resistance.

How to Calculate Armature Current?

Example Problem:

The following example outlines the steps and information needed to calculate Armature Current.

First, determine the source voltage. For this example problem, the source voltage is measured to be 150 volts.

Next, determine the back emf. For this problem, the back emf is measured to be 100 volts.

Next, determine the resistance. The armature resistance is measured as 5 ohms.

Finally, calculate the armature current using the formula above:

Ia = (V-E) / Ra

Ia = (150-100) / 5

Ia = 10 amps