Inductor Energy Calculator
By Santaji GadepatilinUpdated October 27, 2026
An inductor stores energy in its magnetic field while current flows, and releases it when the current changes — which is why switching off a coil can cause a voltage spike. Learn the inductor working principle and the limits set by inductor saturation current. This free inductor energy calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the inductor energy calculator
Enter the inductance and the current to get the stored energy. Add a switch-off time to estimate the voltage spike if the current is interrupted that quickly without suppression.
For more background, read Lenz’s Law and Electromagnetic Induction.
Inductor energy formulas
E = ½ × L × I² · V = L × di/dt
Energy examples
| Inductor | Current | Energy |
|---|---|---|
| 10 µH SMPS inductor | 5 A | 0.125 mJ |
| 100 µH choke | 3 A | 0.45 mJ |
| 10 mH filter choke | 2 A | 20 mJ |
| Relay coil, 1 H | 30 mA | 0.45 mJ |
| Contactor coil, 5 H | 0.2 A | 100 mJ |
| Motor winding, 50 mH | 20 A | 10 J |
Suppressing inductive kick
| Method | Release speed | Notes |
|---|---|---|
| Flyback diode | Slow | Simplest for DC coils; delays relay drop-out |
| Diode + Zener | Fast | Clamps to a set voltage |
| RC snubber | Medium | Works on AC and DC |
| Varistor (MOV) | Fast | Common on AC contactor coils |
Saturation and core choice
Ferrite cores saturate at about 0.3–0.4 T, iron powder and silicon steel at higher flux. Gapped cores store most of the energy in the air gap, which is why SMPS inductors use them.
Frequently asked questions
How much energy does an inductor store?
E = ½ × L × I². A 10 mH inductor carrying 2 A stores 20 mJ.
Why do relay coils need flyback diodes?
When the current is interrupted quickly, the coil tries to keep it flowing, producing a voltage spike of L × di/dt that can reach hundreds of volts and damage transistors. A diode gives the current a safe path.
What is inductor saturation?
Above a certain current the core can hold no more magnetic flux, so inductance falls sharply. Always stay below the saturation current in the datasheet.
Where is inductor energy used?
Switch-mode power supplies store energy in inductors each cycle and release it to the output; ignition coils use it to create high-voltage sparks.