Series & Parallel Resistance

Find equivalent resistance for two resistors in series or in parallel. Clear formulas and steps for circuit homework and electronics practice.

Key formula

Series: R_t = R1 + R2; Parallel: 1/R_t = 1/R1 + 1/R2

About this tool

Series and parallel combinations are the foundation of most resistor networks. This tool shows how equivalent resistance changes when resistors share one path versus multiple paths.

How to use this calculator

1. Choose the variable you want to solve for and confirm which values are already known.
2. Enter inputs in consistent units before calculating so the formula is applied correctly.
3. Check whether the result is physically reasonable by comparing it with the size of the inputs.
4. Use the step-by-step breakdown to see how the equation was rearranged and evaluated.