Parallel and Series Resistor Calculator
List the resistor values separated by commas, spaces or new lines. The calculator returns the total resistance for both a parallel and a series connection.
Result
- Parallel in ohms
- 59.9768 Ω
- Total conductance
- 16.67 mS
- Resistors entered
- 3
Formula
- Parallel: 1 ÷ R_total = 1 ÷ R₁ + 1 ÷ R₂ + 1 ÷ R₃ + …
- Two in parallel: R_total = (R₁ × R₂) ÷ (R₁ + R₂)
- Series: R_total = R₁ + R₂ + R₃ + …
How the Parallel and Series Resistor Calculator works
Resistors in series carry the same current, so their resistances add. Resistors in parallel share the same voltage, so their conductances add. Conductance is the reciprocal of resistance.
The parallel total is always smaller than the smallest resistor in the group. Two equal resistors in parallel give half the value of one.
Worked example
For 100 Ω, 220 Ω and 470 Ω in parallel: 1 ÷ 100 + 1 ÷ 220 + 1 ÷ 470 = 0.016673. The reciprocal is 59.98 Ω. In series the same three total 790 Ω.
Frequently asked questions
How do I calculate two resistors in parallel?
Multiply them and divide by their sum. For 100 Ω and 220 Ω, 100 × 220 ÷ 320 = 68.75 Ω.
Why is parallel resistance lower than any single resistor?
Each added branch gives the current another path. More paths mean more total current at the same voltage, which is the same as lower resistance.
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