Series and Parallel Resistor Calculator

Find the equivalent resistance of any number of resistors connected in series or in parallel.

Series total
Parallel total
Resistors counted

Runs entirely in your browser. Nothing you enter is sent anywhere.

How it works

In series, the same current flows through every resistor, so their resistances simply add up. In parallel, each resistor gives the current another path, so the total is always smaller than the smallest resistor.

The same idea works in reverse for capacitors: capacitors in parallel add up, and capacitors in series combine like resistors in parallel.

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

Worked example

100 Ω, 220 Ω and 330 Ω in series total 650 Ω. In parallel: 1/R = 1/100 + 1/220 + 1/330 = 0.017576, so R = 56.9 Ω, below the smallest 100 Ω resistor.

Frequently asked questions

Why is parallel resistance lower than any single resistor?

Each extra resistor adds another path for current, so for the same voltage more total current flows. More current at the same voltage means lower equivalent resistance.

How do I make a non-standard value from standard resistors?

Combine two standard values. Two equal resistors in parallel give half the value, and two in series give double. Try combinations here until you get close to the value you need.

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