Series Resistors Formula

Series resistor formula is used to sum two or more resistors in a series configuration. Solving two or more resistor/resistive components is very easy. Simply add the numb of resistors to obtain the final equivalent answer.

The table below illustrates the general equation along with a specific case to solve two, three, four and five resistors.

Formulas to solve resistors in series
General formula Req = R1 + R2 + R3 + … + Rn
Formula For 2 Series Resistors Req = R1 + R2
Formula For 3 Series Resistors Req = R1 + R2 + R3
Formula For 4 Series Resistors Req = R1 + R2 + R3 + R4
Formula For 5 Series Resistors Req = R1 + R2 + R3 + R4 + R5

Let’s solve an example to better understand this.

Example # 1: A series circuit contains a 12 V source with a 5 Ω,  a 10 Ω, and 20 Ω resistor. Simplify the circuit by reducing all resistances to the single equivalent resistance.

Solution: Req = R1 + R2 + R3 = 5 Ω + 10 Ω + 20 Ω = 35 Ω

series-resistors-formulaOther formulas:

kW to Amps: Different equations and calculations to find kW in DC, Single, two, and three-phase AC circuits.

kVA to Amps: Different formulas to calculate current from kVA’s.

How to identify components in series?

Two or more components are in series when one end of components share the same node. The figure below displays the simplest possible series circuit with two components.


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