Last updated: 2026-06-15

Energy stored in an inductor

When current flows through an inductor it builds a magnetic field, and that field stores energy. The amount is set by the inductance and the square of the current:

with $L$ in henries, $I$ in amperes and $E$ in joules. This calculator solves for the stored energy, the inductance or the current.

Current, not voltage, drives the energy

An inductor is the magnetic counterpart of a capacitor. A capacitor stores energy in an electric field set up by voltage, $E = \tfrac{1}{2} C V^2$; an inductor stores energy in a magnetic field set up by current, $E = \tfrac{1}{2} L I^2$. Because the dependence is on $I^2$, doubling the current stores four times as much energy.

Worked example

A $10\ \text{mH}$ inductor carries a steady current of $2\ \text{A}$:

Entering an inductance of 10 mH and a current of 2 A reproduces this result.

Why the stored energy matters

The energy in the magnetic field is what makes an inductor resist sudden changes in current. When a switch opens, that energy has to go somewhere: the collapsing field induces a voltage that can greatly exceed the supply, which is why relay and motor circuits use a flyback diode or snubber to absorb it safely. The same stored energy is what an LC circuit trades back and forth with its capacitor to sustain an oscillation.

Limitations

The formula assumes an ideal inductor with a constant inductance. Real inductors with ferromagnetic cores can saturate at high current, where the effective inductance falls and the stored energy no longer follows $\tfrac{1}{2} L I^2$. Winding resistance also dissipates some energy as heat. For high-current or high-frequency designs, consult the inductor's saturation-current and core-loss specifications.