Any number in.
One total resistance.

Series and Parallel Resistance: Formulas and Examples

The equivalent resistance of a resistor network depends on whether the resistors are connected in series or in parallel.

Series Formula

For resistors in series, Rtotal = R1 + R2 + R3 + …. The same current flows through every resistor.

Parallel Formula

For parallel resistors, 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + …. The same voltage appears across each branch.

Example

Two resistors of 220 Ω and 330 Ω in series give 550 Ω. In parallel they give approximately 132 Ω.

How to Use This Calculator

1. Select Series or Parallel.
2. Add the required number of resistors.
3. Enter each resistance value.
4. Read the equivalent resistance shown by the calculator.

Engineering Note

Equivalent resistance is only one part of a real design. Check resistor power rating, voltage rating, tolerance and temperature coefficient before selecting components.

FAQs

Is parallel resistance always lower? For positive resistor values, the equivalent parallel resistance is lower than the smallest individual resistor.

Does series resistance increase? Yes. Series resistances add directly.