How to Calculate Voltage Drop?

We have simple electrical circuits in our house; these circuits contain a source of voltage. Voltage sources are battery, generator, power supply, and the utility wires connect your building with the primary electric circuits.

In the wires, current flow in electrons, while we see these circuits, we notice many branching and re-joining points in these circuits.

Current flow through the wires and circuits is measured in volts. Measurement is called voltage; the rate of flow of current from the circuit is called voltage.

You may know about Voltage drop; what does it mean? It means when the voltage at the end of the wire is lower than the voltage at the start point.

It is a common problem, and it happens with any length of the cable and due to resistance. Voltage increases with the increase in the length of the cable and resistance.

How much is voltage drop acceptable?

The acceptable percentage of voltage drop is 5 %. More than 5 percent voltage drop can cause many problems, such as flickering or dim lights, sometimes due to hot wires burning of circuits or burning appliances in the home.

How many types of circuits in wiring?

The most founding types of circuits in the wiring system are of two types.

  • Series Circuit
  • Parallel Circuit

What is a Series circuit?

Series circuit means current flows in a single path with the support of a single wire. No matter whatever resistances are through the wires, you just add up all the resistances to get the circuit’s total resistance.


Rs= R1+R2+R3…….RN

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How to calculate voltage?

For calculating voltage drop in a series circuit, follow the below process.

First of all, calculate total resistance, which will be calculated by adding all the resistances in the series circuit to get the individual R-value.

After that, you will need to calculate the current flow in the circuit; it will be the same for each resistor because only one wire is used along the complete circuit.

Now Ohm’s law will help you calculate the voltage drop across every resistor in a series circuit.

Suppose you have a power source of 48-V there connected four resistors in the series R1= 4 Ω, R2=4 Ω, R3= 8 Ω, and R4= 8 Ω; how we will calculate the voltage drop?

Calculate the total resistance=4+4+8+8=24 Ω

Now calculate the current in the wire= 48 V/24 Ω= 2A

Next to that, with the help of formula V=IR, calculate the voltage drop for each resistor.

What is a Parallel circuit?

In this circuit, the primary wire is branched into two or more wires, with a separate resistor for each wire—resistance in these circuits calculated as per the below formula.


1/Resistance in parallel circuit = 1/R1+1/R2+1/R3+1/R4….1/RN

How to Calculate Voltage Drop?

If we take the above example, the Voltage drop calculation for a parallel circuit is more straightforward than the series circuit.

There is the same resistance value for the voltage drop across each resistor in the parallel circuit. You can calculate the voltage drop in a simple way, Total voltage divided by several resistors.


Voltage drop = Total voltage/ number of resistors

Voltage drop= 48 V/ 4= 12 V

Method to calculate voltage Drop in a copper wire?

Copper wire is one of the most using things in the circuits; we will detail how to calculate voltage drop in copper wire.

Voltage Drop= Length x Current x 0.017

Length= Total length of the copper wire measure in meters

Area = you will add the cross-sectional area of copper wire in square millimeters.

Current= total current flowing through the copper wire.

  • But this method will only apply to the copper wire when the temperature should be 25 degrees centigrade.
  • 017 is only applicable for copper wire, not suitable for other types of wires.
  • Take measure of the area carefully.


Suppose you want to calculate the voltage drop for a copper wire with a length of 100M, while its area is 4 square millimeters and current flow is 25 A.

Voltage Drop= 100*25*0.017/4=10.62 V

What is an alternative method to calculate the Voltage drop?

The above methods are undoubtedly quite simple, but some people who do not have even little knowledge about physics may face difficulty calculating voltage drop.

A simple and most reliable way to calculate voltage drop in any cable is the voltage drop calculator.

You can work with any of the free available calculators on the web, just enter the required information and get the real and accurate calculations.

There are many types of wires are using in the circuits, such as Silver, copper, Aluminum, iron, and others, so if you do not get a better understanding of the formulas, then try Voltage drop calculators to calculate the exact voltage drop.

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How to use a Voltage Drop Calculator?

You just need to input simple information in the calculator to get the voltage drop in a circuit.

  • First of all, you will need to enter the type of wire, such as Silver, copper, Aluminum, and iron.
  • You will also add the resistivity of the wire.
  • After that, enter the diameter of your wire in a square millimeter.
  • Length of the cable but only adds single side length.
  • You also need to enter the type of phase of the current such as single-phase or triple-phase.
  • Now push the calculate button, you will get the voltage drop and percentage of voltage drop.

How can we manage voltage drop Problems?

Some ways will help you to reduce the voltage drop in the circuit.

  • You should increase the number of the conductor or the size of the conductor.
  • Reduction of length of the conductor can also reduce voltage drop.
  • You can also minimize the voltage drop by decreasing temperature.
  • With the reduction of power load, you can also reduce the voltage drop in a circuit.

Final Thoughts:

Voltage drop is a significant problem for us that affect the performance of our electric appliances.

But we can protect our appliances by correctly calculating voltage drop through formulas or calculator and keeping it in an acceptable range by taking some precautionary measures.

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