Inductor Energy Calculator
Enter an inductance and a current to get the energy stored in the coil's magnetic field — and see why that energy climbs with the square of the current.
Stored energy in one step
Enter the inductance in henries and the current in amperes and the calculator returns the energy stored in the magnetic field (½LI²) in joules.
Use SI units
Inductance in henries and current in amperes give energy in joules — convert millihenries to henries (divide by 1000) before you start.
What is inductor energy?
The energy in a magnetic field
An inductor stores energy whenever current flows through it, holding that energy in the magnetic field that surrounds its coil. The amount grows with the inductance — a measure of how strongly the coil opposes changes in current — and, far more steeply, with the current itself. The inductor energy calculator turns two measurements, the inductance in henries and the current in amperes, into the stored energy in joules. It is the number behind switch-mode power supplies, flyback circuits, and the snappy voltage spikes you see when an inductive load is suddenly disconnected.
Enter an inductance in henries and a current in amperes to get the energy stored in the magnetic field in joules instantly.
The stored energy is half the inductance multiplied by the current squared.
E = ½ × L × I²The current is squared, so it dominates the result: a small change in current produces a large change in energy. The inductance enters only to the first power, so doubling it merely doubles the stored energy at the same current. Use henries and amperes and the energy comes back in joules.
Suppose a 2 H inductor carries a steady current of 3 A.
Square the current
3² = 9 — the squared current that drives the energy.
Multiply by the inductance
2 × 9 = 18 — inductance times current squared.
Take half
½ × 18 = 9 J — the energy stored in the inductor's magnetic field.
The result (9 J for the coil above) is how much energy the inductor is holding in its magnetic field at that instant — energy the circuit must supply to build the field and energy that has to go somewhere when the field collapses. The crucial insight is that the energy scales with the square of the current: double the current from 3 to 6 A and the stored energy jumps fourfold, from 9 to 36 J, while doubling the inductance instead only doubles the energy to 18 J. That square-law dependence on current is why high-current chokes store so much energy and why that energy resists sudden change so forcefully. Because an inductor opposes any rapid drop in current, opening the circuit forces the stored energy out as a sharp voltage spike — the spark across a switch or the kick that destroys an unprotected transistor. Designers tame that energy with flyback diodes, snubbers, and soft-switching, all sized around the joules this formula gives.
The formula is exact, but a couple of practical points are worth keeping in mind.
Ideal inductor and consistent units
This calculator assumes an ideal inductor with a constant inductance and no winding resistance or core saturation. Real cores lose inductance as current rises, so a saturated coil stores less than ½LI² predicts. Keep your units consistent — henries for inductance and amperes for current — or the joules will be wrong: convert millihenries to henries by dividing by 1000 before you enter the inductance.