Inductor Energy CalculatorFree online other calculator — instant results, no sign-up
Calculate magnetic energy stored in an ideal inductor.
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About the Inductor Energy Calculator
The Inductor Energy Calculator calculates the magnetic energy stored in an ideal inductor from its inductance in millihenries and current in amperes. It converts inductance to henries and applies the energy relationship E = ½LI² to report the result in joules. With the default inputs of 10 mH and 2 A, the stored energy is 0.02 J.
- Inductance (mH)
- The inductor's inductance, entered in millihenries (mH), describes its ability to link magnetic flux with current and defaults to 10 mH.
- Current (A)
- The current flowing through the inductor at the instant of interest, entered in amperes (A), defaults to 2 A.
Formula and method
L = L_mH / 1000; E = ½LI² = ½(L_mH / 1000)I². With the default inputs: E = ½ × (10 / 1000) × 2² = 0.02 J.
- EMagnetic energy stored in the ideal inductor, in joules (J).
- LInductance in henries (H), after conversion from millihenries.
- L_mHThe numerical inductance input in millihenries (mH).
- ICurrent through the inductor, in amperes (A).
Divide the inductance input by 1000 to convert millihenries to henries, square the current, and multiply these quantities by one-half. For the default inputs, 10 mH becomes 0.01 H and (2 A)² is 4 A², giving E = ½ × 0.01 × 4 = 0.02 J.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Inductance10 mH
- Current2 A
Results
- Result0.02 J
How to use the Inductor Energy Calculator
- 1Enter the inductance in the Inductance (mH) field; leave it at 10 for the default example.
- 2Enter the current in the Current (A) field; leave it at 2 for the default example.
- 3Check that the inductance is expressed in millihenries rather than henries and that the current is expressed in amperes.
- 4Run the calculation to apply E = ½LI² after the inductance is converted to henries.
- 5Read the Result in joules; the default inputs produce 0.02 J.
Reading your result
The Result row reports the magnetic energy stored at the specified current, in joules (J). For 10 mH and 2 A, Result = 0.02 J. This is stored energy, not power consumption or the energy dissipated as heat.
Limitations
The calculation assumes an ideal, linear inductor with constant, nonnegative inductance. It does not account for winding resistance, core losses, magnetic saturation, hysteresis, or parasitic capacitance. If inductance changes with current, the simple ½LI² relationship may not apply. For varying current, use the instantaneous current to find instantaneous stored energy; using RMS current instead gives average stored energy for an ideal inductor with constant inductance over the same averaging interval. The result alone does not establish safe current ratings or the voltage produced when current is interrupted.
Common questions
Why must the inductance in millihenries be converted before calculating energy?+
The formula E = ½LI² yields joules when inductance is in henries and current is in amperes. The default 10 mH must therefore be entered into the formula as 0.01 H.
How does changing the current affect the stored magnetic energy?+
Energy is proportional to current squared when inductance is constant. Doubling the current quadruples the stored energy, while doubling the inductance only doubles it.
Does reversing the current make the stored energy negative?+
No. Current is squared in E = ½LI², so reversing its direction leaves the stored energy unchanged for the same current magnitude and inductance.
Does a result of 0.02 J mean that all of this energy can be recovered from a real inductor?+
No. For the default 10 mH and 2 A, 0.02 J is the ideal stored magnetic energy. In a real circuit, winding resistance, core losses, and switching losses can reduce the energy delivered to another component.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.