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Energy Stored in an Inductor

The magnetic energy stored in the field of a current-carrying inductor.

Written by the Vorzep Team

Circuit AnalysisEnergy Storage

Energy Stored in an Inductor Calculator E = ½ L I²

E = ½ · L · I²
E = energy (J)  ·  L = inductance (H)  ·  I = current (A)
⟹ Solve ⟷ E, L, I
J
H
A
Please fix the errors above.
Solve for:
Presets:
Stored Energy —
—
E: — L: — I: —
✓ Copied!
Energy Gauge —
Low (< 1 mJ) Medium (1 mJ – 1 J) High (> 1 J)
E = ½ L I²  ·  Energy stored in the magnetic field. All values must be non‑negative.

Variables

SymbolQuantityUnit
EEnergyJ
LInductanceH
ICurrentA

What it means

The energy stored in an inductor is given by E = ½ L I², where L is the inductance and I is the current flowing through it. This energy is stored in the magnetic field around the coil. Similar to capacitors, the energy depends on the square of the current. Inductors are used to store energy in power supplies, in transformers, and in motors. The stored energy is released when the current decreases, which can cause voltage spikes (back EMF). Understanding the stored energy is important for designing flyback converters, relay drivers, and for protecting circuits from inductive kickback. The energy density of inductors is typically lower than capacitors, but they are essential in AC applications. Example: An inductor of 10mH carrying 5A stores E = 0.5 * 0.01 * 5² = 0.5 * 0.01 * 25 = 0.125 joules (125 mJ).

Worked example

Energy Stored in an Inductor – Practical Example

Real‑World
Scenario: A 10 mH inductor carries a current of 2 A. Calculate the stored magnetic energy.
ParameterValue
L10 mH = 0.01 H
I2 A
FormulaE = ½·L·I²
1Substitute:E = 0.5 × 0.01 × 2²
22² = 4, so:E = 0.5 × 0.01 × 4 = 0.02 J
Final Design E = 20 mJ ✓ Energy stored in magnetic field
Why: Energy in an inductor is proportional to the square of the current – higher current stores more energy.

Common mistakes

  • Units: L in henries, I in amperes → E in joules.
  • Energy stored: Proportional to the square of the current – doubling current quadruples energy.
  • Alternative: E = ½·L·I² – no other form.
  • Sign: Positive.
  • Magnetic field: Energy is stored in the magnetic field around the inductor.

Applications

Energy stored in an inductor is E = ½·L·I², depending on inductance and the square of current. This energy is stored in the magnetic field and is released when the current decreases. Engineers use this formula to design inductors for power supplies, to calculate the energy in relay and solenoid coils, and to ensure that the energy is safely dissipated during switching. In switched‑mode power supplies, the stored energy is transferred to the output. In motor drives, it contributes to torque. By understanding the energy relationship, professionals can select inductors with adequate current ratings and design snubber circuits to protect switches.

  • Inductor design for switching regulators and converters
  • Energy‑recovery circuits and flyback converters
  • Relay and solenoid coil energy management
  • Motor control and drive design
  • Safety considerations for inductive loads