Series & Parallel Resistor Calculator

Combine up to four resistors in series or parallel to get the equivalent resistance in ohms.

Ω
Ω
Ω
Leave at 0 if not used.
Ω
Leave at 0 if not used.
Equivalent resistance (parallel)
68.75 Ω
Resistors combined
2
Equivalent conductance
0.0145455 S

Estimate generated with SortedSums: https://sortedsums.com/resistor-calculator/. For informational purposes only; verify before relying on it.

How it’s calculated

In series the same current flows through every resistor, so resistances add. In parallel every resistor sees the same voltage, so conductances (1/R) add and the total is always smaller than the smallest resistor.

Series: R = R1 + R2 + R3 + R4 Parallel: 1/R = 1/R1 + 1/R2 + 1/R3 + 1/R4

Example: 100 Ω and 220 Ω in parallel give 1 ÷ (1/100 + 1/220) = 22,000 ÷ 320 = 68.75 Ω. In series they give 320 Ω.

Frequently asked questions

What is the shortcut for two resistors in parallel?

Product over sum: R = R1 × R2 ÷ (R1 + R2). For 100 Ω and 220 Ω that is 22,000 ÷ 320 = 68.75 Ω.

What about identical resistors in parallel?

n identical resistors R in parallel give R ÷ n. Two 1 kΩ resistors in parallel make 500 Ω.

How do I handle a mixed series-parallel network?

Reduce it step by step: combine each parallel group to one equivalent, then add the series parts, and repeat.

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Sources

Formulas are taken from the free public references above. Results are provided “as is” for informational and educational purposes only. See our disclaimer.

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