Series/Parallel Resistance Calculator
Enter two or more resistor values and choose series or parallel to get the total resistance the circuit sees.
Total resistance
Series vs. parallel, at a glance
Series and parallel are the two basic ways to wire resistors together, and they behave like opposites. Series resistances always add up to something bigger than the largest individual resistor, because current has to push through every one of them in turn. Parallel resistances always combine to something smaller than the smallest individual resistor, because current gets to split across multiple paths.
Most real circuits use a mix of both, so being able to reduce a network down to a single equivalent resistance — working from the innermost series or parallel groups outward — is a core circuit-analysis skill.
Frequently Asked Questions
How do I combine resistors in series?
In series, resistors are wired end to end so the same current flows through all of them, and their resistances simply add: R_total = R1 + R2 + R3 + .... Three 100Ω resistors in series give 300Ω.
How do I combine resistors in parallel?
In parallel, resistors are wired side by side so the same voltage appears across each, and their reciprocals add: 1/R_total = 1/R1 + 1/R2 + .... The result is always smaller than the smallest individual resistor — two 100Ω resistors in parallel give 50Ω.
Why is the parallel total always smaller than any single resistor?
Adding a parallel path gives current an extra route, so the combined resistance to that current is lower than any one path alone — similar to opening a second checkout lane shortening the total wait, not lengthening it.
Which should I use in a real circuit?
Series is common for dropping voltage across multiple points or building a voltage divider. Parallel is common for combining battery capacity, matching a target resistance from stock values, or splitting current between multiple LEDs or loads.
Educational tool only. Real resistors carry manufacturing tolerance, so measure the built circuit with a multimeter for anything precision-critical.