Resistor CalculatorFree online other calculator — instant results, no sign-up
Series and parallel resistance (values separated by commas).
About the Resistor Calculator
The Resistor Calculator computes the total equivalent resistance for any set of resistors arranged in series and in parallel. It is useful for electronics hobbyists, students, and engineers designing circuits or combining available stock components to achieve target resistance values.
- Resistances (Ω)
- A list of individual resistor values in ohms (Ω), separated by commas or spaces; values must be positive numbers.
Formula and method
Series: R_series = R_1 + R_2 + ... + R_n; Parallel: R_parallel = 1 / ((1 / R_1) + (1 / R_2) + ... + (1 / R_n))
- R_seriesTotal equivalent resistance when connected in series (Ω)
- R_parallelTotal equivalent resistance when connected in parallel (Ω)
- R_1, R_2, ..., R_nIndividual resistance values in ohms (Ω)
The input string is parsed by commas and spaces to extract positive numbers. For the series configuration, values are summed directly; for parallel, the reciprocal of each resistance is summed to find total conductance, which is then inverted to yield equivalent resistance. Both results are rounded to 3 decimal places.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Resistances (Ω)100, 220, 470
Results
- Series790 Ω
- Parallel59.977 Ω
How to use the Resistor Calculator
- 1Enter individual resistance values in ohms (Ω) separated by commas or spaces.
- 2The tool parses the input and filters out zero, negative, or non-numeric entries.
- 3Series resistance is calculated by adding all individual values together.
- 4Parallel resistance is calculated by summing the reciprocals (1/R) and inverting the sum.
Reading your result
Series resistance is always higher than the largest individual resistor because current must traverse each element sequentially. Parallel resistance is always lower than the smallest resistor in the network because each parallel path offers an additional route for electrical current.
Limitations
The calculator assumes ideal linear resistors and does not account for component manufacturing tolerances, temperature coefficients, or power dissipation limits. It also evaluates strictly all-series or all-parallel connections, not hybrid series-parallel network topologies.
Common questions
Can I enter values using kilohms (kΩ) or megohms (MΩ)?+
No, enter all values in standard ohms (Ω). For example, enter 4.7 kΩ as 4700 and 1 MΩ as 1000000.
What happens if I enter zero or negative numbers?+
The calculator filters out zero and negative values before computing the results, preventing division by zero errors in the parallel calculation.
Why is the equivalent parallel resistance smaller than any single resistor?+
Each resistor in parallel provides an additional branch for current to flow, increasing total conductance across the nodes and lowering overall resistance.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.