Series and Parallel Inductor Calculator (Equivalent Inductance)

How do inductors combine?

Inductors with no magnetic link between them follow the same rule as resistors. Inductances add in series, and reciprocals add in parallel.

Series

L_eq = L1 + L2 + … + Ln

The same current flows through every inductor. The result is larger than the largest inductor.

Parallel

1 / L_eq = 1 / L1 + 1 / L2 + … + 1 / Ln

Every inductor has the same voltage across it. The result is smaller than the smallest inductor. For two inductors the shortcut is L1 × L2 / (L1 + L2).

Example

10 mH, 22 mH and 47 mH in series give 79 mH. The same three in parallel give 1/10 + 1/22 + 1/47 = 0.1667, so the equivalent is 6.0 mH.

Magnetic coupling

These rules hold only when the magnetic fields of the inductors do not interact. For coils on a shared core or placed side by side the mutual inductance M matters. Two series coils give L = L1 + L2 + 2M when the fields aid and L = L1 + L2 − 2M when they oppose. The tool does not include M.

Stored energy

When a current is entered the energy stored in the equivalent inductance is E = ½ × L × I². Opening the circuit of a current carrying inductor releases that energy as a high voltage spike.