Series Resistor Calculator
Enter two or more resistor values to get the series equivalent — a straight sum, with the biggest resistor's voltage share shown.
Last updated: 2026-09-28
How the calculation works
- Series resistances simply add — the same current flows through every element.
- Voltage divides proportionally: the biggest resistor takes the biggest share of the supply.
- The percentage row shows the dominant element's share at a glance.
Formula
R_eq = R₁ + R₂ + ... + Rₙ
| Symbol | Meaning | Unit |
|---|---|---|
R_eq | Equivalent series resistance | Ω |
Worked example
Interpreting the result
Series adds resistance (and inductance, and capacitor ESR); parallel adds conductance. Series is how you build values you cannot buy, share voltage across elements, or add current limiting. Two caveats: tolerance stacks (±5% parts in series make ±5% of the sum, not of each), and power rating stays per-element — each resistor dissipates its own I²R share.
Assumptions
- Ideal resistors in a single series path.
- Same current through every element (true series connection).
Limitations
- No stray effects (lead inductance/capacitance) at high frequency.
- Not for mixed series-parallel networks — reduce them in stages.
Frequently asked questions
What is the formula for resistors in series?
Just add them: R_eq = R₁ + R₂ + … The same current flows through all; voltages divide in proportion to each resistance.
When should I use series instead of parallel?
Series when you need a bigger resistance or to split voltage/power across elements; parallel when you need smaller resistance or to share current.