Inductor Series/Parallel Calculator
Add up to five inductors in series and in parallel at the same time, and see the combined inductance both ways in millihenries.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter each inductor value in millihenries (mH) — you can fill anywhere from two to five boxes.
- Leave unused inductor boxes blank.
- Read the series total (values added) and the parallel total (reciprocals added), plus how many inductors were combined.
How it works
Inductors combine like resistors. In series the total inductance is just the sum, Lₜ = L1 + L2 + …, so the result is always larger than any single inductor. In parallel the reciprocals add, 1/Lₜ = 1/L1 + 1/L2 + …, so the total is always smaller than the smallest inductor. The tool computes both totals from whichever values you enter (two or more) and reports the count used. It assumes the inductors are not magnetically coupled.
Worked example
Worked example. Two 100 mH inductors: in series Lₜ = 100 + 100 = 200 mH; in parallel 1/Lₜ = 1/100 + 1/100 = 2/100, so Lₜ = 50 mH. With 60, 30 and 20 mH: series = 110 mH, parallel = 10 mH.
Common mistakes
- Using the parallel (reciprocal) formula for a series connection, or vice versa — series adds directly, parallel adds reciprocals.
- Assuming the coils are independent when they are close together; mutual coupling changes the effective inductance and these formulas no longer apply.
- Entering values in different units — keep every inductor in millihenries (mH) so the totals are consistent.
Frequently asked questions
Why is the parallel total smaller than the smallest inductor?
Adding reciprocals always yields a larger reciprocal sum, whose inverse is smaller than any single term — exactly as with resistors in parallel.
Do these formulas account for mutual inductance?
No. They assume no magnetic coupling between the coils. If the inductors share flux, the mutual inductance M and whether the fields aid or oppose must be included, so keep the coils separated or shielded.
How many inductors can I combine?
Up to five at once. Enter at least two values; leave the remaining boxes blank and they are ignored.
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Tip: Enter any known values to calculate the remaining results.
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