Series & Parallel Inductor Calculator

Inductors in series and parallel

For ideal inductors with no mutual coupling, the series total is just the sum: Ltotal = L₁ + L₂ + … + Ln, identical to resistors. In parallel, sum the reciprocals: 1/Ltotal = 1/L₁ + 1/L₂ + … + 1/Ln. When two coils sit close enough to share flux, mutual inductance M matters: L = L₁ + L₂ ± 2M in series (sign depends on whether windings aid or oppose). Energy stored is E = ½ · L · I² in joules, and inductive reactance in AC is XL = 2π · f · L in ohms. Example: two 10 mH coils in series with no coupling give 20 mH; in parallel, 5 mH. With 50% coupling (M = 5 mH) in series-aiding, you get 30 mH; series-opposing, 10 mH.

Applications: filters, chokes and transformers

Combined inductances appear in LC filters (radio tuning, EMI suppression), smoothing chokes in linear power supplies, motor chokes for AC drives, loop antennas, and magnetic recording heads. Transformers are the deliberate use of mutual inductance: tightly coupled primary and secondary windings transfer power at a turns ratio.

FAQ

Why do inductors in series add like resistors? Both impede current flow proportionally to their value; in series the same current passes through each, and induced voltages add.

What if I ignore mutual inductance? Safe when coils are far apart, orthogonal, or shielded. Stack coils close on the same axis and M can change the total by tens of percent.

Does inductance change with frequency? Ideally no, but parasitic capacitance and core losses cause real inductors to have a self-resonant frequency above which they behave capacitively.

Can I mix air-core and ferrite coils? Yes, but watch for saturation in the ferrite, which collapses inductance under high current.