Inductor Energy Calculator
Calculate energy stored in an inductor from its inductance and current. Solve for any of E, L, or I using E = ½·L·I².
How to Use
- Pick solve target: energy, inductance, or current.
- Use suffixes: nH/µH/mH/H for inductance, mA/A for current, mJ/µJ for energy.
- Visual shows a magnetic field intensity proportional to stored energy.
- Unlike a capacitor (electric field), an inductor stores energy in its magnetic field.
Show Work
Formulas
History of Magnetic Energy Storage
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.
About This Calculator
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.
About the Inductor Energy Calculator
The Inductor Energy Calculator gives you a fast, free answer for electronics and circuit design without sending anything off your device. Calculate energy stored in an inductor from its inductance and current. Solve for any of E, L, or I using E = ½·L·I².
How it works
Enter your figures and the result appears instantly, updating the moment you change anything. There is no submit button and nothing to wait for, so it is easy to try a few what-if numbers and compare the results. Just check each box holds the kind of value it expects.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
How does an inductor store energy?
Current through an inductor creates a magnetic field around (and inside the core of) the coil. Energy is stored in this field. When the current source is removed, the field collapses and drives current back through the circuit. The inductor behaves as a current source trying to maintain its previous current.
Why the ½ in the formula?
Same reason as capacitor energy: you\'re integrating from zero to I. Work done charging from 0 to I is W = ∫₀ⁱ L·i di = ½·L·I². The ½ appears in every quadratic integral like this.
What happens during flyback?
If you suddenly open a switch carrying inductor current, the inductor tries to maintain current and generates a voltage spike limited only by parasitic capacitance or a flyback diode. Without protection, voltages of hundreds or thousands of volts can appear — useful for ignition systems, destructive for sensitive components.
Buck vs boost energy cycles?
Buck: inductor charges during switch-on (storing energy), discharges through diode during switch-off (transferring to output). Boost: inductor charges with input current during switch-on, dumps energy through diode to a higher-voltage output during switch-off. Both exploit L·I² storage.
Inductor vs capacitor storage?
Capacitor stores in electric field: E = ½CV². Inductor stores in magnetic field: E = ½LI². Capacitors are voltage devices; inductors are current devices. Supercaps beat inductors for energy density; inductors beat caps for instantaneous power.
How do I use the Inductor Energy Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Flyback Converter
1 mH inductor at 2A: E = 2 mJ. Stored energy dumped into output during switch-off.
Ignition Coil
Automotive coil: 5 mH, 8A → 160 mJ stored. Switched off rapidly to create 30kV spark voltage.
Coilgun / Railgun
Large inductor banks: 1 mH at 1000A → 500 J per shot. Released briefly through projectile.
EMI Filter Choke
100 µH at 10A: E = 5 mJ. Energy returned to circuit during current ripple, not dissipated.
Buck Converter Inductor
22 µH at 2A in a 5V→3.3V buck: E = 44 µJ cycled at switching frequency.
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