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Series & Parallel Resistor Calculator
Calculate the total resistance of up to six resistors connected in series and in parallel, in ohms, kilohms or megaohms.
How to use it
- Enter each resistor value in ohms (1 kΩ = 1000, 1 MΩ = 1000000).
- Leave unused resistors at 0.
- Read the total for a series connection and for a parallel connection.
How it works
In series the resistances add: R = R1 + R2 + … In parallel the conductances add: 1/R = 1/R1 + 1/R2 + …; the total is always smaller than the smallest resistor. Two equal resistors in parallel give half the value.
For two resistors in parallel you can use the shortcut R = (R1 × R2) ÷ (R1 + R2). Power dissipation splits across parallel resistors in inverse proportion to their values, which is why parallel combinations are handy to reach a higher wattage rating.
FAQ
How do you calculate parallel resistance?
Add the reciprocals of the resistors and take the reciprocal of the sum: for 1 kΩ and 2.2 kΩ, 1/R = 0.001 + 0.000455 = 0.001455, so R = 687 Ω.
Why is parallel resistance smaller than any single resistor?
Each extra path gives current another way through, so the total opposition falls.
Can I use resistors of different power ratings together?
Yes, but check each one: in series each carries the same current, in parallel each carries current in proportion to 1/R, so the lowest-power part may overheat first.
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