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Resistor Series & Parallel Calculator

Add any number of resistors and get both the series (sum) and parallel (reciprocal) equivalent resistance, with SI-prefix input.

Enter each resistor value in ohms. SI prefixes and RKM notation accepted:4k7, 220, 1M. Blank rows are ignored.

Series total (R₁ + R₂ + …)–
Parallel total (1 / Σ 1/R)–
Resistors used–
SeriesParallel
Series resistances add; parallel always gives less than the smallest

Combining resistors

Resistors in series carry the same current, so their resistances add. Resistors in parallel share the same voltage, so their conductances (1/R) add — giving a total that is always smaller than the smallest resistor.

Series: R = R₁ + R₂ + … + Rₙ

Parallel: 1/R = 1/R₁ + 1/R₂ + … + 1/Rₙ

For just two resistors in parallel this simplifies to the "product over sum" rule: R = R₁·R₂ / (R₁ + R₂). Two equal resistors in parallel give half the value; N equal resistors give R/N.

Why it matters

Series and parallel combinations let you reach a value you don't have in stock from resistors you do, or spread power dissipation across several parts. Need a specific ratio instead? Try thepotential divider calculator.

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