Enter the electromotive force, current, and load resistance into the calculator to determine the internal resistance.

Internal Resistance Formula

The following formula is used to calculate an internal resistance. 

r = (e / i) - R
  • Where r is the internal resistance (ohms)
  • e is the electromotive force (Volts)
  • i is the current (amps)
  • R is the resistance of the load in the circuit.

To calculate internal resistance, divide the electromotive force by the current, then subtract the resistance of the load.

Internal Resistance Definition

Internal resistance is the total resistance to electron flow that arises from the internal structures of a circuit.

Internal Resistance Example

How to calculate the internal resistance?

  1. First, determine the electromotive force.

    For this example we will say this value is 10 V.

  2. Next, determine the current.

    For this example we will assume a current of 10 amps.

  3. Next, determine the load resistance.

    For this example the value is 20 ohms.

  4. Finally, calculate the internal resistance.

    Using the formula we find the internal resistance to be: 10/10 – 20 = -19 ohms.