Parallel Resistor Calculator

It can be quite tiresome to calculate the equivalent resistance or REQ of parallel resistors manually. Fortunately, this parallel resistor calculator can help you with the calculations no matter how many resistors you have in parallel. You can also choose to perform the calculations by hand then use the parallel circuit calculator to check your answer.

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How to use the parallel resistor calculator?

Intimidating as the calculations for parallel resistors may seem, using this parallel resistor calculator is the exact opposite. This online tool is very easy to use and understand. Here are the steps to follow for using this equivalent resistance calculator or parallel resistance calculator:

  • First, enter the value of Resistor 1.
  • Then enter the values of Resistor 2, Resistor 3, Resistor 4, and Resistor 5.
  • After entering all of the required values, the parallel circuit calculator automatically generates the result you need. Since the unit of measurement for all the resistor values is Ω, the final result also has this same unit of measurement.

What is a parallel resistor?

When you connect both terminals of the resistors together in parallel, this means that you have respectively connected the each of the terminals to the other resistor or resistors. Unlike other circuits, you can also classify a circuit with parallel resistors as a current divider.

This is because parallel resistor circuits can take more than a single path since they have several paths to allow the current to pass through. Since this type of circuit provides multiple paths for the current supply to flow through, the strength of the current might not be the same across all of the branches or paths.

But the voltage drop which occurs across all the resistors in a parallel circuit remains the same. This means that parallel resistors share a common voltage and this fact applies to all the elements connected in parallel.

By definition, a parallel resistive circuit is one where the resistors have parallel connections or they share the same nodes or points of connection. Also, this type of circuit has more than just one path connected to a single voltage source.

How do you calculate resistance in a parallel circuit?

The main feature which characterizes a parallel circuit is the common voltage or potential difference across the ends of all the resistors. Even without using an equivalent resistance calculator, you can calculate the equivalent resistance for this type of circuit using this formula:

1/R = 1/R1 + 1/R2 +… + 1/Rn


R refers to the equivalent parallel resistance
R1, R2, … Rn refers to the resistances of individual resistors numbered 1…n.

The unit of measurement of all these values is Ω or Ohms. By definition, one Ohm is the electrical resistance between two given points. When you apply a potential difference of 1 volt to these points, it produces a 1-ampere current. Therefore:

1Ω = 1V / 1A or

Ω = kg * m^2 / (s^3 * A^2) in SI base units

Here are some steps to follow for the calculation of parallel resistance without using a parallel resistance calculator:

  • First, determine the resistance values of all the resistors connected in parallel. For instance, let’s have three resistor values of , , and .
  • Substitute these values in the formula we gave above:

1/R = 1/4 + 1/3 +1/6

therefore, 1/R = 0.75 while R = 1.33

  • To check the accuracy of your answer, input the values in the parallel resistor calculator.

How do I calculate resistance?

Before you can perform the calculation, you must have a good understanding of the parallel circuits first. Remember that this kind of circuit divides into several paths then join together once again. Also, keep in mind that current flows through each of the circuit’s individual paths.

If the circuit comes with resistors on the main branch or if a single branch comes with more than one resistor, you should perform a different calculation. Solve for the total resistance using the resistance value of each of the branches. Each of the resistors slows down the current which passes through a single branch.

But the resistors don’t have that much of an effect on the overall circuit resistance. Therefore, you must use the total resistance formula which is:

1/RT = 1/R1 + 1/R2 + 1/R3 + 1/R4 … 1/Rn


R1 refers to the resistance of the 1st branch
R2 refers to the resistance of the 2nd branch
R3 refers to the resistance of the 3rd branch
R4 refers to the resistance of the 4th branch
and so on until you reach the final branch Rn.

This is the simplest way to calculate resistance. But in some cases, you might not have the values of the individual resistances. In such a case, you need to use the voltage and the current instead. Here are the steps to follow:

  • In parallel circuits, the voltage across a single branch has the same value as the total voltage which flows throughout the whole circuit. If you know the voltage value of one of the branches, you can perform the calculation.
  • You can also find the value of the total voltage as it’s equal to the power source of the circuit, like a battery. In parallel circuits, currents differ from one branch to another. You must know the value of the total current. Without it, you can’t calculate the total resistance.
  • As soon as you have the total voltage and current, you can compute for the total resistance through Ohm’s Law:

R = V / I.

  • Look out for any branches which have zero resistance. If a parallel circuit has one such branch, all the current flows through this branch and the resistance becomes zero.

Why is equivalent resistance less in parallel?

As you keep on adding resistors to a parallel circuit, this decreases the equivalent resistance of the entire circuit. However, this also increases the circuits overall current. This happens because adding resistors in parallel provides the circuits with more paths for the current to flow.