Enter an inductor's inductance and instantaneous current to calculate its ideal stored magnetic energy in microjoules and joules.
Advanced options
Optional datasheet screen
This is an ideal constant-inductance result. It is energy, not power.
This compares the operating current with the Isat rating you entered. It is not proof that the inductor is suitable.
Positive is below the entered rating. Negative is above it.
Values above 100% are above the entered rating.
This is the same ideal energy in the base SI energy unit.
Table of contents
How to use our Inductor Energy Calculator
- Choose the unit printed beside the inductance, then enter the inductance number.
- Choose the unit used for the current value, then enter the instantaneous current. For maximum energy in a pulsed circuit, use peak inductor current.
- Select "Advanced options" if you want to compare that current with a datasheet saturation-current rating. Enter the Isat value and unit from the exact inductor datasheet.
- Select "Calculate". The first result is ideal stored magnetic energy in uJ, followed by the same value in J.
- If you entered Isat, check the saturation-current screen. Negative headroom means the operating current is above the entered rating.
- If you change a unit after entering a value, the displayed number converts to preserve the same physical quantity. For a newly copied value, choose its unit first.
Definitions
Inductance: A property of an inductor that determines how much magnetic energy it stores for a given current. It is measured in henries (H).
Instantaneous current: Current through the inductor at one moment. Stored energy depends on the square of this current.
Microjoule (uJ): One millionth of a joule.
Saturation current (Isat): A datasheet current rating related to magnetic-core saturation. Its exact definition and test conditions depend on the manufacturer and part.
Current headroom: The signed percentage difference between the entered Isat rating and operating current. Positive is below the rating, zero is equal, and negative is above it.
Common mistakes and quick fixes
Mistake: Entering a value marked mH or uH while "H" is selected.
Fix: Select the engineering prefix printed beside the inductance before entering the number.
Mistake: Using average current when checking maximum stored energy in a pulsed circuit.
Fix: Enter the peak instantaneous inductor current for the operating point you want to check.
Mistake: Reading joules as watts.
Fix: Joules measure stored energy. Watts measure the rate of energy transfer.
Mistake: Treating a current below Isat as proof that the inductor is suitable.
Fix: Also check the exact datasheet conditions, temperature, current ripple, losses, and other ratings for the circuit.
Limitations & Key Assumptions / Boundary Conditions
- The calculation assumes an ideal inductor with constant inductance at the entered current.
- Actual inductance can change with DC bias, temperature, frequency, tolerance, and core material.
- The optional Isat screen compares one operating current with one entered datasheet rating. It does not predict temperature rise, copper loss, core loss, voltage stress, transient behavior, or circuit stability.
- Isat definitions and test conditions vary by manufacturer and part, so use the datasheet for the exact inductor.
- Enter current magnitude only. Zero current correctly gives zero stored energy.
Methodology
Energy calculation
The calculator converts inductance to henries and current to amperes before calculating ideal magnetic energy. Energy rises in direct proportion to inductance and with the square of instantaneous current.
E (stored energy in J) = 0.5 × L (inductance in H) × I^2 (current in A)
The joule result is multiplied by 1,000,000 to show microjoules.
Energy in uJ = Energy in J × 1,000,000
Worked example
For 10 mH and 1 A, inductance is 0.01 H. The ideal stored energy is 0.5 × 0.01 × 1^2 = 0.005 J, or 5,000 uJ.
Optional saturation-current screen
When you enter an Isat rating, the calculator converts it to amperes and compares it with the same current used in the energy equation.
Headroom (%) = 100 × (Isat - I) / Isat
Entered Isat being used (%) = 100 × I / Isat
Current at or below the entered Isat produces the at-or-below screen. Current above it produces an above-rating screen and negative headroom.