Inductor Energy Calculator

Joseph Henry's 1830 discovery of self-inductance (independently of Faraday) identified the inductor as the magnetic counterpart to the capacitor: both store energy, one in electric fields, one in magnetic fields. The energy formula E = ½LI² comes directly from integrating power P = V·I = L·I·(dI/dt) from zero to full current — the same quadratic integral that gives ½CV² for capacitors. James Clerk Maxwell formalized both in his 1873 Treatise.

Magnetic energy storage dominated the earliest high-power electrical applications. Induction coils (large inductors switched by interrupter contacts) powered X-ray tubes in the 1890s and early radio spark-gap transmitters through the 1920s, releasing hundreds of joules per spark. The automotive ignition coil — invented by Charles Kettering at DELCO in 1910 to replace magneto ignition — is conceptually identical: ~5 mH primary, 8 A steady-state, switched off abruptly to dump stored magnetic energy into a secondary that produces 30 kV across the spark plug gap.

Modern switching power supplies transfer energy through the same mechanism thousands of times per second. A buck converter charges its inductor during switch-on, then lets it discharge through a diode during switch-off; a flyback converter does the same with galvanic isolation through a coupled transformer. Every watt flowing into every laptop charger, LED driver, and DC-DC module you own is being ferried across that inductor in packets of ½LI² joules.

Pick what to solve for (energy, inductance, or current), enter the other two with standard suffixes, and this tool returns the third via E = ½·L·I². The visualization shows magnetic field intensity proportional to stored energy, plus flux linkage Ψ = L·I in volt-seconds.

Safety note: opening a switch carrying inductor current without a flyback diode lets V = L·dI/dt spike to whatever voltage is needed to maintain the current — easily hundreds or thousands of volts from a tiny coil. Useful for spark ignition; destructive for MOSFETs. Everything runs in your browser; no values leave the page.