Series and Parallel Resistor Calculator
List your resistors to get the total resistance in series or parallel, and with a supply voltage, the current and power in each one.
- In series
- In parallel
- Total current
- Total power
- Each Resistor
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| Name | Resistors | Connection | Total | Remove |
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Series and Parallel Resistance
Resistors in series sit end to end, so the current passes through each one in turn and their resistances add up. Resistors in parallel sit side by side, giving the current several paths, so the total is less than the smallest resistor.
For just two resistors in parallel there's a shortcut: R = (R₁ × R₂) ÷ (R₁ + R₂), product over sum. Two equal resistors in parallel give half the value of one.
Worked Example
100 Ω, 220 Ω and 470 Ω in series add to 790 Ω. In parallel, 1 ÷ 100 + 1 ÷ 220 + 1 ÷ 470 = 0.01 + 0.004545 + 0.002128 = 0.016673, and 1 ÷ 0.016673 = 59.98 Ω, less than the 100 Ω resistor.
Current and Power in Each Resistor
In series, every resistor carries the same current, and the voltage splits in proportion to resistance. In parallel, every resistor sees the full voltage, and the current splits, with most going through the smallest resistor. Check each resistor's power, V × I, against its rating.
Tips
To make a value you don't have, combine standard ones: two 1 kΩ resistors in series make 2 kΩ, and in parallel make 500 Ω. Capacitors combine the opposite way: they add in parallel and follow the reciprocal formula in series.