Series & Parallel Resistor Calculator
Instantly calculate the total equivalent resistance of your circuit. Supports multiple resistors in series or parallel configurations.
Calculate Equivalent Resistance
Enter your resistor values and select the configuration to instantly find the total resistance of your network.
Circuit Configuration
Define your resistor network parameters below.
How it Works
Understanding resistor networks
Series Circuits
Resistors are connected end-to-end. The same current flows through each, and the total resistance is simply the sum of all individual values (R_total = R1 + R2 + …).
Parallel Circuits
Resistors are connected across the same two points. The voltage is the same across each, but current divides. Total resistance is always less than the smallest resistor.
Unit Conversion
The calculator automatically converts all inputs into base Ohms (Ω) before performing the mathematical operations to ensure perfect accuracy.
Smart Formatting
The final result is intelligently scaled back to the most readable unit (Ω, kΩ, or MΩ) for easy interpretation in your schematic or bill of materials.
Resistor Reference Data
A quick reference guide for resistor units, multipliers, and standard E-Series values.
| Unit | Symbol | Multiplier (in Ohms) | Common E12 Values |
|---|---|---|---|
| Ohm | Ω | 1 | 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 |
| Kilo-ohm | kΩ | 1,000 | 1.0k, 1.2k, 1.5k, 2.2k, 3.3k, 4.7k, 5.6k, 6.8k |
| Mega-ohm | MΩ | 1,000,000 | 1.0M, 1.2M, 1.5M, 2.2M, 3.3M, 4.7M |
| Milli-ohm | mΩ | 0.001 | Used for current sensing (e.g., 10mΩ, 50mΩ) |
Resistor Networks FAQ
Answers to the most frequently asked questions about series and parallel resistor calculations.
For resistors connected in series, the total equivalent resistance is simply the sum of all individual resistances. The formula is R_total = R1 + R2 + R3 + … + Rn. The current remains the same through each resistor, but the voltage drops across each one.
For resistors connected in parallel, the reciprocal of the total equivalent resistance is equal to the sum of the reciprocals of each individual resistance. The formula is 1/R_total = 1/R1 + 1/R2 + 1/R3 + … + 1/Rn. The voltage remains the same across each resistor, but the current divides among them.
The total equivalent resistance of a parallel circuit is always less than the value of the smallest individual resistor in that circuit. Adding more resistors in parallel provides additional paths for current to flow, thereby decreasing the overall resistance.
In a series circuit, if one resistor fails (opens), the entire circuit is broken and current stops flowing everywhere. In a parallel circuit, if one branch fails, current continues to flow through the other remaining branches, so the rest of the circuit keeps working.