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Electronics Projects: How to Combine Resistors in Series and Parallel

By Doug Lowe

Resistors can be combined to form complex electronic networks in which some of the resistors are in series and others are in parallel. For example, a network of three, 1 kΩ resistors and one 2 kΩ resistor are arranged in a mixture of serial and parallel connections.


The way to calculate the total resistance of a network like this is to divide and conquer. Look for simple series or parallel resistors, calculate their total resistance, and then substitute a single resistor with an equivalent value.

For example, you can replace the two 1 kΩ resistors that are in series with a single 2 kΩ resistor. Now, you have two, 2 kΩ resistors in parallel.

Remembering that the total resistance of two resistors with the same value is half the resistance value, you can replace these two, 2 kΩ resistors with a single 1 kΩ resistor. You’re now left with two, 1 kΩ resistors in series. Thus, the total resistance of this circuit is 2 kΩ.

Project 2-2 lets you do a little hands-on work with some simple series and parallel resistor connections so you can see firsthand how the calculations described in the previous three sections actually work in the real world.

You’ll probably find that due to the individual variations of actual resistors (due to their manufacturing tolerances) the calculated resistances don’t always match the resistance of the actual circuits. But in most cases, the variations aren’t significant enough to affect the operation of your circuits.

In this project, you will assemble five resistors into three different configurations. The first has all five resistors in series. The second has them all in parallel. And the third creates a network of two sets of parallel resistors that are connected in series.