Calculate energy stored in an inductor using E = ½LI². Includes time constant, inductive reactance, impedance, and L/R current rise visualization.
An inductor stores energy in its magnetic field when current flows through it. The energy stored is E = ½LI², where L is the inductance in henries and I is the current in amperes. This energy is released when the current decreases, which is why inductors resist changes in current — they are the electrical analog of mechanical inertia.
This Inductor Energy Calculator computes the stored energy from inductance and current values. It also analyzes the L/R time constant (how quickly current rises or falls in an inductive circuit), the inductive reactance at a given frequency, and the total impedance of a series R-L circuit. A current-rise visualization shows how the current approaches its steady-state value over multiple time constants.
Whether you are designing a power supply filter, analyzing a relay coil, sizing an energy-storage inductor, or studying electromagnetic theory, this calculator provides all the essential inductor parameters in one place.
Inductor calculations span multiple formulas: energy storage, time constant, reactance, and impedance. This calculator combines them all, including a visual time-constant chart showing how current builds up in an L/R circuit. It is especially useful for power electronics design and circuit analysis. Keep these notes focused on your operational context.
Stored Energy: E = ½ × L × I² Time Constant: τ = L / R Inductive Reactance: X_L = 2πfL Impedance: |Z| = √(R² + X_L²) Current Rise: I(t) = (V/R)(1 − e^(−t/τ)) Where: L = inductance (H) I = current (A) R = resistance (Ω) f = frequency (Hz)
Result: 0.125 J (125 mJ)
An inductor with L = 10 mH carrying 5 A stores E = ½ × 0.01 × 25 = 0.125 J (125 mJ) of energy in its magnetic field.
The energy stored in an inductor resides in its magnetic field. The energy density of a magnetic field is u = B²/(2μ₀), and integrating over the volume of the inductor gives E = ½LI². This is analogous to the energy stored in a capacitor (E = ½CV²) and in a spring (E = ½kx²) — all are quadratic in the relevant state variable.
When a DC voltage is applied to a series RL circuit, the current rises exponentially: I(t) = (V/R)(1 − e^(−t/τ)). The time constant τ = L/R determines the speed of this rise. Large inductors with small resistance take longer to reach steady state. This transient behavior is critical in relay timing, motor starting, and power supply design.
Inductors are fundamental components in switching power supplies (buck, boost, buck-boost converters), where they alternately store and release energy each switching cycle. The inductance value, saturation current rating, and core losses determine converter performance. Proper inductor selection is often the most critical design decision in a power supply.
Current flowing through an inductor creates a magnetic field. Energy is stored in this field. When the current is interrupted, the collapsing field releases the stored energy, often producing a voltage spike.
The L/R time constant (τ = L/R) is the time it takes for current in an RL circuit to reach about 63.2% of its final value. After 5τ, the current is within 0.7% of steady state.
Inductive reactance X_L = 2πfL is the opposition to AC current flow. It increases with frequency, so inductors pass low frequencies and block high frequencies — the opposite of capacitors.
No. Practical inductors store millijoules to joules. Superconducting magnetic energy storage (SMES) systems can store megajoules, but they are far more complex and expensive than batteries for bulk energy storage.
An inductor resists changes in current (V = L × di/dt). When a switch opens abruptly, di/dt becomes very large, producing a high voltage spike. Flyback diodes are used to suppress these spikes in relay and motor circuits.
Energy is in joules (J). For small inductors, millijoules (mJ) or microjoules (μJ) are more convenient.