how to find total resistance in a parallel circuit

Parallel Resistor Calculator

Created by Bogna Szyk and Álvaro Díez

Reviewed by

Steven Wooding

Last updated:

May eleven, 2022

Table of contents:

Resistors in parallel formula
How to calculate parallel resistance
Other uses of the parallel resistor calculator
FAQ

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 spring to the series resistor computer.

Resistors in parallel formula

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

$1/R = 1/R_1 + 1/R_2 + ... + i/R_n$

where:

$R$ is the equivalent parallel resistance
$R_1, R₂, ..., R_n$ are the resistances of individual resistors numbered $1, two, ..., northward$ .

The units of all values are Ohms (symbol: Ω). 1 Ohm is defined as electric resistance between two points that, when applied with a potential departure of 1 volt, produces a current of ane ampere. Hence, i Ω = i V / i A or, in SI base units, Ω = kg·grand²/(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 unlike modes. The commencement mode allows y'all to calculate the total resistance equivalent to a group of private resistors in parallel. In contrast, the second mode allows you to gear up the desired total resistance of the bunch and calculate the one missing resistor value, given the rest.

To go along it simple, we but show y'all a few rows to input numbers, but new fields will magically announced as you need them. Y'all can input upwards to x resistors in total.

Permit's wait at an example for the second, slightly more complicated, fashion:

Select Calculate missing resistor under Mode.
Now input the full resistance you desire your circuit/collection of resistors to accept.
Get-go past introducing the values of the resistors you already know (new fields will appear every bit needed).
The calculator automatically gives you the required missing resistor after each input.

Other uses of the parallel resistor figurer

The principle is the same as when determining capacitance in series or induction in parallel – you lot tin can utilise it for these calculations likewise. Just remember that the units are not the same!

If you would similar to find out the value of power dissipated in the resistor, try the Ohm'south law calculator or Resistor wattage computer.

FAQ

How do you lot summate 2 resistors in parallel?

Take their reciprocal values, add together the two together and accept the reciprocal once more. For instance, if i resistor is 2 Ω and the other is four Ω, then the calculation to find the equivalent resistance is 1 / (1/two + 1/4) = 1 / (3/4) = iv/3 = 1.33.

Is the voltage the same in a parallel circuit?

Yes, the voltage across all the components is the aforementioned in a parallel circuit.

Why does resistance subtract in parallel?

This phenomenon happens considering the current has many more paths that it could take. Imagine a shop opens up several new check-out tills. The overall resistance to people going through the check-out will decrease as the workload is shared in parallel.

How do you detect an unknown resistor in a parallel circuit?

Rearrange the parallel resistor formula 1/R = 1/R₁ + 1/R₂ + ... + 1/R_{due north} in terms of R_n , given that yous know the desired overall resistance. That gives you R_{due north} = (1/R - i/R₁ + 1/R₂ + ...)^-ane .

For instance, if you take R₁ = 4, R₂ = 2 and want R = one, then R₄ = ane / (i - i/4 - i/2) = 4 Ω.

Bogna Szyk and Álvaro Díez