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:
Ris the equivalent parallel resistance
R₁, R₂, ... Rnare the resistances of individual resistors numbered
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).
The formula for resistors in parallel is similar to the formula for inductors in parallel.
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:
- Select "Calculate missing resistor" under Mode.
- Now input the total resistance you want you circuit/collection of resistors to have.
- Start by introducing the values of the resistors you already know (new fields will appear as needed).
- 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.