Inductors in Series Calculator

Total series inductance, stored energy and reactance.

What it does

Inductors in series add up like resistors, as long as their magnetic fields do not couple.

Where it's used

Building an inductance you don’t have and designing filters.

How to use it

Type the values separated by commas, e.g. 100u, 47u.
Enter the current to see stored energy.
Set a frequency to see the reactance.

The formula explained

L_total: L1 + L2 + … + Ln (no coupling)
E: ½LI², energy stored in the magnetic field
X_L: 2πfL, opposition to AC

Worked example

Inputs:

Inductor values (comma separated): 100u, 47u H
Current: 2 A
Frequency (reactance): 100k Hz

The calculator gives:

Total inductance: 147 µH
Stored energy: 294 µJ
Reactance XL at 100 kHz: 92.36 Ω

Tips and common mistakes

Mount inductors apart or at right angles, otherwise coupling changes the total.
The current rating is set by the inductor with the lowest saturation current.
Reactance rises with frequency, so inductors block high frequencies.

Questions people ask

What if the inductors are magnetically coupled?

Then the total becomes L = L1 + L2 ± 2M, where M is the mutual inductance: plus when the fields aid each other, minus when they oppose. This calculator assumes no coupling (M = 0).

How is the reactance worked out?

X_L = 2π × f × L. The example’s 147 µH at 100 kHz gives about 92.4 Ω. Reactance rises in step with frequency, which is why inductors pass DC and block high-frequency noise.

What happens when an inductor saturates?

Above its saturation current the core can’t store more magnetic energy, so the inductance falls sharply and the current rises much faster than expected. In a switching supply that can overheat or destroy the switch, so stay below the saturation rating.

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