Series and Parallel Resistor Calculator
Enter your resistor values in ohms and choose series or parallel to get the total resistance. Series resistance is the sum of the values, while parallel resistance is the reciprocal of the sum of reciprocals.
How to use the resistor calculator
- Enter one resistance value per line, in ohms.
- Choose whether the resistors are wired in series or in parallel.
- Read the total resistance, recalculated as you edit the values.
Examples
Three resistors in series
100, 200, 300 ohm, series
600 ohm
Two resistors in parallel
60, 40 ohm, parallel
24 ohm
Frequently asked questions
How do you add resistors in series?
Add the values together. Resistors in series share the same current, so the total resistance is R1 + R2 + ... + Rn.
How do you add resistors in parallel?
Take the reciprocal of the sum of reciprocals: 1 / R_total = 1/R1 + 1/R2 + ... The total is always smaller than the smallest resistor.
What is the parallel resistance of two equal resistors?
Exactly half of one of them. Two 100 ohm resistors in parallel give 50 ohm, since 1 / (1/100 + 1/100) = 50.
Can I mix series and parallel groups?
Solve each group on its own first. Combine a parallel block into a single value, then add it in series with the rest, repeating as needed.
Why must values be greater than zero?
A zero-ohm value is a short circuit and a negative resistance is not physical, so both are rejected to keep the parallel formula well defined.
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