Resistor Combination Calculator
Calculate total resistance for resistors combined in series or parallel.
Assumptions used in this calculation
- Ideal resistors: Assumes ideal resistive components with no tolerance, temperature drift or parasitic inductance/capacitance.
About this calculator
Combining resistors in series is a simple sum, but parallel combinations require adding reciprocals and then inverting the result again, a step that's easy to fumble by hand, especially with three resistors at once, and a wrong total resistance can throw off current calculations or damage a circuit designed around a specific load. This calculator takes up to three resistor values and your chosen configuration, then applies the correct formula: a straight sum (R = R1 + R2 + R3) for series, or the reciprocal formula (1/R = 1/R1 + 1/R2 + 1/R3) for parallel, returning the single equivalent resistance either way. It's built for anyone designing or troubleshooting a circuit, whether combining standard resistor values to hit a non-standard target resistance, calculating the load seen by a power supply, or checking a breadboard prototype before powering it on, without needing to remember or rearrange the parallel-resistance formula from memory each time.
Worked example
100Ω and 220Ω in parallel
Result: 68.75 Ω
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