Series and Parallel Resistance Calculator
Combine ideal resistor values using the correct relationship for a simple series or parallel connection.
How to use this calculator
- Enter positive resistance values separated by semicolons and type either series or parallel.
- Check that every input uses the stated units and covers the same period, population or project scope.
- Change one assumption at a time when comparing scenarios.
Formula used by series parallel resistance calculator
Series: Rₑq = ΣR; parallel: 1/Rₑq = Σ(1/R)
- Series: Rₑq = ΣR; parallel: 1/Rₑq = Σ(1/R)
- Only pure series or pure parallel networks are covered; mixed networks need to be reduced section by section.
- Inputs are validated against the tool-specific constraints; displayed results are rounded for readability.
Worked examples
Worked example
Three resistors can be combined as a series sum or a parallel reciprocal sum; the connection mode changes the answer.
The tool parses a semicolon-separated resistor list and applies the selected connection.
The tool parses a semicolon-separated resistor list and applies the selected connection.
Understanding the result
Combine ideal resistor values using the correct relationship for a simple series or parallel connection.
Only pure series or pure parallel networks are covered; mixed networks need to be reduced section by section.
Important notes
Only pure series or pure parallel networks are covered; mixed networks need to be reduced section by section.
Treat the result as an estimate for the assumptions entered; verify important specifications against the relevant source or professional guidance.
Frequently asked questions
Why is parallel equivalent resistance lower?
Each parallel branch provides an additional path for current, so total conductance increases.
Can I enter a mixed circuit?
Not directly. Reduce each series/parallel section and calculate the simplified network step by step.
How should I use this result?
Enter positive resistance values separated by semicolons and type either series or parallel.
Related calculators
- Series Resistance Calculator — Add two to four ideal resistances connected in series.
- Parallel Resistance Calculator — Calculate equivalent resistance for two or three resistors connected in parallel.
- LED Series Resistor Calculator — Estimate LED series resistance and power dissipation from supply voltage, forward voltage and target current.
- Conductor Resistance from Resistivity Calculator — Estimate conductor resistance from material resistivity, length and cross-sectional area with unit conversion.
- Thermal Resistance Layers Calculator — Combine positive thermal resistance values in series and calculate the reciprocal overall U-value.
- Capacitor Combination Calculator — Calculate equivalent capacitance for two or more ideal capacitors connected in series and in parallel.
Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- Ohm's Law — Understand Ohm's law and the relationship between voltage, current, and resistance.
- Voltage Drop — Understand voltage drop and how current and resistance affect a basic voltage-drop estimate.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.