Resistors in Series/Parallel Calculator
Calculate total resistance for up to 5 resistors in series or parallel.
Returns equivalent resistance with worked examples and per-resistor bar chart.
Resistors in series and parallel are the two fundamental circuit configurations. Understanding how to calculate equivalent resistance is essential for every electronics project.
Series formula:
R_total = R1 + R2 + R3 + ... + Rn
Parallel formula (two resistors):
R_total = (R1 × R2) / (R1 + R2)
Parallel formula (general — n resistors):
1/R_total = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn
What each variable means:
- Series — resistors connected end-to-end; the same current flows through all; voltages add up
- Parallel — resistors connected side-by-side sharing the same two nodes; the same voltage applies to all; currents add up
- R_total — the single equivalent resistance that the source “sees”
Worked examples:
Series: Three resistors: 100 Ω, 220 Ω, 470 Ω R_total = 100 + 220 + 470 = 790 Ω
Parallel (two): 1 kΩ and 1 kΩ in parallel: R_total = (1,000 × 1,000) / (1,000 + 1,000) = 1,000,000 / 2,000 = 500 Ω Two equal resistors in parallel always give half the value of one.
Parallel (three): 100 Ω, 200 Ω, 400 Ω: 1/R = 1/100 + 1/200 + 1/400 = 0.01 + 0.005 + 0.0025 = 0.0175 R_total = 1 / 0.0175 = 57.1 Ω
Key rules to remember:
- Series total is always larger than the largest individual resistor
- Parallel total is always smaller than the smallest individual resistor
- Adding a resistor in parallel always reduces total resistance
- Adding a resistor in series always increases total resistance
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.