Enter the total voltage drop and the resistance into the calculator to determine the amp drop.

Amp Drop Formula

The following formula is used to calculate an amp drop.

a = V  * P 
  • Where a is the amperage drop
  • V is the voltage drop
  • P is the wattage being supplied over the wire

To calculate an amp drop, multiply the voltage drop by the wattage.


What is an amperage drop?

An amp drop is a measure of the drop in voltage and current that occurs over the length of a wire due to the internal resistance of the wire. The amp drop is directly proportional to the voltage drop.

Example Problem

How to calculate an amp drop?

The following example problem examines the steps and information required to calculate the amp drop across a wire.

First, determine the voltage drop. This is done using the resistance and distance that the electricity is moving across the wire. For this example, the voltage drop is 10 volts.

Next, determine the total power in wattage being supplied to the wire across the distance. In this case, the wattage is 20 watts.

Finally, calculate the amps drop using the formula above:

a = V * P

a = 20 * 10

a = 200 amps