🔗 Series & Parallel Resistor Calculator
Enter a list of resistor values and get the total resistance both in series (added up) and in parallel (the reciprocal rule).
In series (end to end)
650 Ω
R₁ + R₂ + … (adds up)
In parallel (side by side)
56.9 Ω
always less than the smallest
3 resistors: 100 Ω, 220 Ω, 330 Ω
Resistors in series add up (R = R₁ + R₂ + …). In parallel the reciprocals add: 1/R = 1/R₁ + 1/R₂ + …, so the total is always smaller than the lowest single resistor. Two equal resistors in parallel give exactly half their value. 🔒 In your browser.
How the series & parallel resistor calculator works
Resistors in series carry the same current and their resistances simply add: R = R₁ + R₂ + …. Resistors in parallel share the same voltage, and their conductances add, so the total is the reciprocal of the summed reciprocals: 1/R = 1/R₁ + 1/R₂ + …. The parallel total is always smaller than the smallest individual resistor. Type any number of values separated by commas, spaces or new lines and both totals update instantly.
Combining resistors is how you reach values that aren't made as standard parts — put two in series or parallel to hit a target. Two equal resistors in parallel give exactly half the value; two equal in series give double. Power sharing differs too: series resistors share voltage, parallel ones share current.
Frequently asked questions
How do I calculate resistors in series?
Add them up: R = R₁ + R₂ + R₃ + …. Three resistors of 100, 220 and 330 Ω in series total 650 Ω. Series resistors carry the same current and their voltages add.
How do I calculate resistors in parallel?
Add the reciprocals and invert: 1/R = 1/R₁ + 1/R₂ + …. For 6 Ω and 3 Ω in parallel, 1/6 + 1/3 = 1/2, so R = 2 Ω — always less than the smallest resistor.
What is the parallel resistance of two equal resistors?
Exactly half. Two 100 Ω resistors in parallel give 50 Ω. In general, N equal resistors in parallel give R ÷ N.
Why is parallel resistance smaller than the smallest resistor?
Adding a parallel path gives current another route, so more current flows for the same voltage — which means lower total resistance. Each extra resistor can only lower it further.
Can I mix series and parallel?
Yes, by working in stages: reduce each parallel cluster to a single value with this tool, then add those in series (or vice-versa). Break the network into series and parallel blocks and combine them step by step.