Parallel Resistor Calculator

By Bogna Szyk and Álvaro Díez
Last updated: May 21, 2021

The parallel resistor calculator is a tool for determining the equivalent resistance of a circuit with up to five resistors in parallel. Read on or jump to the series resistor calculator.

Resistors in parallel formula

A parallel circuit is characterized by a common potential difference (voltage) across the ends of all resistors. The equivalent resistance for this kind of circuit is calculated according to the following formula:

1/R = 1/R₁ + 1/R₂ +... + 1/Rn

where:

  • R is the equivalent parallel resistance
  • R₁, R₂, ... Rn are the resistances of individual resistors numbered 1...n.

The units of all values are Ohms (symbol: Ω). 1 Ohm is defined as electrical resistance between two points that, when applied with a potential difference of 1 volt, produces a current of 1 ampere. Hence, 1 Ω = 1 V / 1 A or, in SI base units, Ω = kg·m²/(s³·A²).

How to calculate parallel resistance

The parallel resistor calculator has two different modes. The first mode allows you to calculate the total resistance equivalent to a group of individual resistors in parallel. In contrast, the second mode allows you to set the desired total resistance of the bunch and calculate the one missing resistor value, given the rest.

To keep it simple, we only show you a few rows to input numbers, but new fields will magically appear as you need them. You can input up to 10 resistors in total.

Let's look at an example for the second, slightly more complicated, mode:

  1. Select "Calculate missing resistor" under Mode.
  2. Now input the total resistance you want you circuit/collection of resistors to have.
  3. Start by introducing the values of the resistors you already know (new fields will appear as needed).
  4. The calculator automatically gives you the required missing resistor after each input.

Other uses of the parallel resistor calculator

The principle is the same as when determining capacitance in series or induction in parallel - you can use it for these calculations too. Just remember that the units are not the same!

If you would like to find out the value of power dissipated in the resistor, try the Ohm's law calculator.

Bogna Szyk and Álvaro Díez
drawing of resistors in parallel in an electrical circuit
Mode
Calculate equivalent resistance
Resistor 1 (R₁)
Ω
Resistor 2 (R₂)
Ω
You can add up to 10 resistors, fields will appear as you need them.
Results
Input at least one resistor to obtain a result.
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