Resistors in Series and Parallel Calculator
Enter two or more resistor values to find their combined resistance if wired in series, and if wired in parallel.
Separate values with commas or spaces. Works for any number of resistors.
How series and parallel resistance work
Resistors in series simply add up: total resistance = R1 + R2 + R3 + ... — the same current flows through each one in turn, and each adds its own resistance to the path.
Resistors in parallel combine differently, since current splits between them: 1/total = 1/R1 + 1/R2 + 1/R3 + ... The parallel total is always smaller than the smallest individual resistor, since adding more paths for current always makes it easier for current to flow overall.
Frequently asked questions
Why is parallel resistance always less than any single resistor?
Adding resistors in parallel gives current more paths to flow through, which always decreases the total opposition to current flow — so the combined resistance is always less than the smallest resistor in the group.
What's the formula for two resistors in parallel?
For exactly two resistors, there's a shortcut: R_total = (R1 × R2) / (R1 + R2), which is equivalent to the general reciprocal formula but quicker to compute by hand.
Does the order of resistors matter?
No — for both series and parallel combinations, the total resistance is the same regardless of the order the resistors are listed in or physically arranged.