If your circuit is tripping again and again- you have to calculate the resistance. If you see short circuits often in your house- you must calculate the resistance.

With this calculation, you can learn how the device or material is reducing the electric current flow. Determine the condition of your circuit or component by calculating the total resistance! But how to calculate total resistance in a Series Parallel circuit! We have the easiest solutions!


Step by Step Calculating the Resistance in Series Circuit 

Well, identifying a series circuit is the easiest. If you see a circuit that has one single loop, it is a series circuit. Unlike the parallel or combination circuits, this one doesn’t have any branches or branching parts.

There are resistors in this circuit but they are not placed here and there. In the series circuit, the resistors of the circuit are positioned in a line. By calculating a resistance, you can learn about the condition of the circuit. If it is weak, take a look at how to prevent circuit breaker from tripping!

Method 1: Adding the Resistances

As we said, the series circuits are easier than the other circuits. So, how to calculate total resistance in a series circuit? Simple, add all of them up! All you need to do is add all the resistances of your circuit. Here, each resistor carries the same current. And so, the sum of all the resistance will be the total resistance of the series circuit.


Let’s make this easier for you. Suppose you have a series circuit that has three resistors of respectively 2 Ω, 5 Ω, and 7 Ω. And so, the total resistance will be the addition of all these resistances.

Resistance R= 2+5+7= 14 Ω

Method 2: Total Current and Voltage

There are chances that you don’t know the resistance of the individual resistors. If you are thinking that you cannot find out the resistance without this, you are wrong! You can also work with the total current and the total voltage and find out the resistance!

Step 1: Count the Total Current

The series circuits have the same amount of current at all points. So, learning about the total current is easy here. All you need is to know the current at any point of the circuit and you are ready! You can simply use it as the total current in your formula to know the resistance. Once you have found it, go for the voltage.

Step 2: Count the Total Voltage

Though the total current of a series circuit is equal to the current at any point, the voltage cannot be measured in the same way. In the case of the voltage, the voltage across the component is not equal to the total voltage.

So, when it comes to counting the total voltage, you can rely on the voltage of the supply of the battery. The voltage of the battery or the supply will be the same as the total voltage of a series circuit. After you have found it out, get ready for counting the resistance.

Step 3: Do the Math

Now that you have found both the total current and the total voltage, get ready to work with the formula. As you don’t know the resistance of the individual resistors, you can simply settle for Ohm’s Law and find out the Resistance R.

V = IR

R = V/I

Here, all you need is to put the value of the total current in the place of I and the total voltage in the place of V. If a series circuit has a

The total current supply of a series circuit is I = 8 amps

And it is powered by a battery of V = 12 Volt


According to the formula-

R = V/I = 12/8 = 1.5 Ω 

So, the total resistance is 1.5 Ω here.

Step by Step Calculating the Resistance in Parallel Circuit 

First of all, you have to go through the parallel circuit and comprehend it. There are multiple paths of a parallel circuit.

And the specialty of a parallel circuit is all the multiple paths of the circuit eventually join back together at a point. And electricity will flow through all the branches of your parallel circuit. There are two points where a parallel circuit can have a resistor. 

  • At times, the circuit might have resistors on the main path. This area is right after or before the branched area of the circuit.
  • On the other hand, there can be two or more resistors added. These resistors are added to a single branch.

For the two types of resistors, there are different methods of calculating the total resistance of the circuit.

Method 1: Adding the Individual Resistances

Your first job here is to calculate the resistance of every branch. As we have already told you, there will be more than one resistor, every resistor will slow electricity passing. However, each one of them will work with one branch only.

And if you count the slowing volume of one branch or one resistor, it will not affect the total resistance of the circuit too much. For counting the total resistance of each branch, there is a formula. Check out the formula first.

1/RT = 1/R1+ 1/R2+ 1/R3+….+ 1/Rn

In this formula, R1 is the resistance of the circuit’s first brand. Here, 2, 3, 4, and n refer to the resistance of all the branches. For example, R1 and R2 is the resistance of the first and second branch, R3 is the resistance of the third brand and finally, Rn is the resistance of the last brand. No matter how many branches are there, all you need to do is count them and set the formula there.

Here, we will give you an example of a parallel circuit. We are taking a parallel circuit with three branches in total. The resistances of the branches respectively are-

R1= 10 Ω or Ohm

R2= 2 Ω or Ohm

R3= 1 Ω or Ohm

Let’s put all of these numbers in our formula and find out the resistance.

1/RT = 1/R1+ 1/R2+ 1/R3+….+ 1/Rn

1/RT= 1/10 + 1/2 + 1/1

1/RT = 0.1 + 0.5 + 1

1/RT = 1.6

RT = 1/1.6

RT = 0.625 Ω or Ohm


Method 2: Total Current and Voltage

At times, you might not know the individual resistance. Well, don’t worry; we have ways to help you out! In this case, the best thing you can do is go for the total current. And then, you have to count the total voltage.

Step 1: Count the Voltage

As we are dealing with the parallel circuit, it makes one thing easy for us. If you know the total voltage across one branch, it’s easy to find out the total voltage across the unit too. Both voltages are the same. This means the amount of voltage across the unit will be the same amount of voltage across the branch and vice versa. So, finding out the voltage of one branch will be enough for getting the result.

Step 2: Count the Current

As we said, it’s easy for you to count the total voltage across one branch; things are not easy when it comes to counting the current. In the parallel circuit, the current across each branch can be different. In this case, counting the total current is necessary. If you want to know about the resistance, count the total current, and then you can move on with it.

Step 3: Do the Math

Once you are done counting the total voltage and the total current, it’s time to follow the formula. To find the resistance, here, you can follow Ohm’s law. Through ohms law, if you know the total Voltage or V and the total Current or I, you can easily get the Resistance or R.


R= V/I

Here, if-

The total voltage of a parallel circuit is V= 9 volts and,

The total current of a parallel circuit is I= 3 amps

Then, the Resistance R according to the formula will be-

R= V/I


R= 3 Ω or Ohm

So, the total Resistance or RT here is 3 Ohm.

The Outcome

Now, let’s talk about the times when you get to see zero resistance (0.) In some cases, one branch of your parallel circuit might have no resistance at all! Yes, this is possible. And if it happens, all of the current will flow through that specific branch with zero resistance. In this case, the resistance of the circuit will be zero ohms.


Note: So, what do zero ohms resistance of a circuit refer to? Well, if you are talking about the resistor of your parallel circuit, you must understand that the resistor has failed.

It will be clearer to say that it is short-circuited or bypassed. As this one has zero resistance, there will surely be a high current. As a result, it will eventually damage the circuit’s other parts added there.

Wrap Up

Counting resistance in the series circuits is easier than the parallel circuits. However, if you know the resistance, for the series circuits, all you need is to add them up. In the case of the parallel one, you have to add the individuals and then follow the formula. But then again, knowing the total current and voltage can be your savior here. Follow any of these methods!

Similar Posts