Inductors in Series and Parallel Calculator
Equivalent inductance of up to four uncoupled inductors in series or parallel, with the inductive reactance at a frequency, the current in each inductor and the magnetic energy stored.
How it works
Series: L = L₁ + L₂ + … (same current) · Parallel: 1/L = 1/L₁ + 1/L₂ + … (current splits as Iₖ = I·L/Lₖ) · X_L = 2π·f·L · E = ½·L·I² · assumes no mutual inductance between the coils
Inductors combine like resistors: in series the induced voltages add, so the inductances add; in parallel the same voltage drives every coil and the reciprocals add, giving less than the smallest inductor. The rules hold when the coils are magnetically isolated — if their fields couple, the mutual inductance M adds or subtracts 2M per pair depending on the winding direction. The reactance X_L = 2πfL gives the AC opposition of the combination. Formulas follow OpenStax University Physics Vol. 2 (chapter 14) and Electronics Tutorials.
Worked example
Inductors of 4.7 mH, 10 mH and 22 mH in series add to L = 36.70 mH. At 1,000 Hz the reactance is 2π × 1,000 × 0.0367 = 230.59 Ω, and with 0.5 A flowing the stored energy is ½ × 0.0367 × 0.5² = 4.587 mJ. Each inductor carries the full 0.5 A; the 22 mH coil holds the most energy, 2.750 mJ.
Sources: OpenStax University Physics Vol. 2 — Mutual Inductance and Self-Inductance · Electronics Tutorials — Inductors in Series and in Parallel
Frequently asked questions
Do inductors add like resistors?
Yes, as long as they are not magnetically coupled: series inductances add and parallel ones combine by reciprocals.
What changes if the inductors are coupled?
Mutual inductance M appears. Two coupled coils in series give L₁ + L₂ ± 2M (plus when the fields aid, minus when they oppose). Keep coils apart or at right angles to avoid coupling.
How does the current split between parallel inductors?
In inverse proportion to inductance, like resistors: Iₖ = I × L_eq / Lₖ. The smallest inductor carries the most current.
Why combine inductors at all?
To reach a value that is not available off the shelf, to share current between parts, or to split heat dissipation in power filters.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.