Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Parallel equivalent (Ω)
68.750
Series equivalent (Ω)
320.00
Resistors used
2
Parallel ÷ series
0.2148
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter r1 (Ω).
- 2Enter r2 (Ω).
- 3Enter r3 (0 to skip) (Ω).
- 4Enter r4 (0 to skip) (Ω).
- 5Read your parallel equivalent (ω) on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Series adds; parallel takes the reciprocal sum. Leave a resistor at zero to skip it.
Worked example
Using the values the calculator loads with:
Inputs
- R1: 100 Ω
- R2: 220 Ω
- R3 (0 to skip): 0 Ω
- R4 (0 to skip): 0 Ω
Results
- Parallel equivalent (Ω): 68.75
- Series equivalent (Ω): 320
- Resistors used: 2
- Parallel ÷ series: 0.2148
What each field means
Inputs
- R1 (Ω)
- The r1 used in the calculation, measured in Ω. Starts at 100 Ω so you have a working example on load.
- R2 (Ω)
- The r2 used in the calculation, measured in Ω. Starts at 220 Ω so you have a working example on load.
- R3 (0 to skip) (Ω)
- The r3 (0 to skip) used in the calculation, measured in Ω. Starts at 0 Ω so you have a working example on load.
- R4 (0 to skip) (Ω)
- The r4 (0 to skip) used in the calculation, measured in Ω. Starts at 0 Ω so you have a working example on load.
Results
- Parallel equivalent (Ω)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Series equivalent (Ω)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Resistors used
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Parallel ÷ series
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the resistor combination calculator work?
Series adds; parallel takes the reciprocal sum. Leave a resistor at zero to skip it. The underlying maths is: Series: R = ΣR. Parallel: 1/R = Σ(1/Rᵢ)
What do I need to enter?
4 values: r1, r2, r3 (0 to skip), and r4 (0 to skip). Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the parallel equivalent (ω) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Parallel & Series Resistor Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/resistor-parallel
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/resistor-parallel" target="_blank" rel="noopener">Parallel & Series Resistor Calculator — RevenueLab</a> (2026).</p>
Source: [Parallel & Series Resistor Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/resistor-parallel) (2026).