Series & Parallel Resistance Calculator
Combine any number of resistors in series or parallel to find their total resistance.
How it works
Chain resistors end to end and they're in series — the total is simply the sum. Three resistors of 100, 200, and 300 ohms in series add up to 600 ohms. Easy.
Wire them side by side across the same two points and they're in parallel, where the total is always less than the smallest resistor. The formula is 1 divided by the sum of each resistor's reciprocal, so those same three resistors come out to about 54.5 ohms.
Add or remove rows to match your circuit and flip the toggle between series and parallel. Blank or zero entries are ignored, so you can leave a slot empty while you're still deciding.
Frequently asked questions
Why is parallel resistance always smaller?
Adding a parallel path gives current another route, so more current flows for the same voltage — and more current for the same voltage means less resistance overall. Every resistor you add in parallel lowers the total.
Can I mix series and parallel groups?
This tool handles one group at a time. For a mixed network, solve the parallel sections first, then feed those totals back in as series values (or the other way around).
What if two resistors are identical in parallel?
Two equal resistors in parallel give exactly half the value — two 100-ohm resistors make 50 ohms. N identical resistors in parallel give the single value divided by N.