Series vs Parallel Resistors

Resistors can be connected in two fundamental configurations. In series, they share the same current and their resistances add directly. In parallel, they share the same voltage and their combined resistance is always less than the smallest individual resistor.

Formulas

Series: R_total = R1 + R2 + R3 + …

Parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3 + … For two resistors: R_total = (R1 × R2) / (R1 + R2)

How to Use This Calculator

Select series or parallel mode, enter as many resistor values as needed, and the total resistance is calculated instantly. You can mix and match values to achieve a target resistance.

Practical Examples

Series Example: 100Ω + 220Ω + 470Ω = 790Ω total.

Parallel Example: Two 1kΩ resistors in parallel = 1000 × 1000 / 2000 = 500Ω.

Practical use: Standard resistor values are limited. Combining two common values lets you hit a precise target. E.g., to get 150Ω: use 100Ω and 50Ω in series, or two 300Ω resistors in parallel.

Why This Matters

• Current limiting: Series resistors increase total resistance to limit current.
• Power sharing: Parallel resistors share the current, reducing power dissipation per resistor.
• Impedance matching: Parallel/series combinations tune circuits to specific frequencies or impedances.
• Prototyping: Quickly calculate combinations from available stock.