Inductor Calculator calculates inductive reactance, series RL impedance and current, stored magnetic energy, and RL time constant using practical electrical units.
Inductor Calculator formulas
RL impedance: Z = √(R² + XL²)
Current: I = V ÷ Z
Energy: E = ½LI²
Time constant: τ = L ÷ R
Inductive reactance increases with frequency and inductance. In a series RL circuit, resistance and reactance combine geometrically because their voltage effects are out of phase.
Worked examples
A 10 mH inductor at 1 kHz has 62.8319 Ω reactance. A 100 mH inductor carrying 2 A stores 0.2 J. A 100 mH inductor with 50 Ω series resistance has a 2 ms time constant.
Choosing an inductor
Check inductance tolerance, DC resistance, rated current, saturation current, core material, temperature, package size and self-resonant frequency. Real components also include core loss and parasitic capacitance, especially at high frequency.
This calculator is for planning and education. It does not replace circuit measurement, simulation, manufacturer instructions or qualified engineering review.
Understanding inductor calculations
An inductor stores energy in a magnetic field while current flows through its winding. This Inductor Calculator helps with four common design questions: how strongly an inductor opposes alternating current, how a series RL circuit affects current and phase, how much magnetic energy is stored, and how quickly current changes after switching. The Inductor Calculator uses ideal formulas that provide a useful starting point for filters, power supplies, relays, motors, audio circuits and classroom exercises.
Reactance and frequency
Inductive reactance is measured in ohms. Doubling frequency doubles reactance, and doubling inductance has the same effect. For that reason, an inductor may pass low-frequency signals while offering much more opposition at high frequency. Enter inductance in microhenries, millihenries or henries and choose hertz, kilohertz or megahertz to avoid manual conversions.
Series RL circuit results
In a series RL circuit, resistance and inductive reactance cannot be added directly because their voltages are out of phase. The Inductor Calculator combines them as perpendicular components to find impedance. It then divides RMS voltage by impedance to estimate RMS current and reports the phase angle. The ideal model assumes a sinusoidal steady-state source and does not include parasitic capacitance or frequency-dependent core loss.
Energy and time constant
Stored magnetic energy depends on inductance and the square of current, so current has a strong effect on the result. The RL time constant indicates how quickly ideal current rises or decays. After one time constant, a rising current reaches about 63.2 percent of its final value; after five time constants, it is effectively settled for most practical estimates.
Practical limitations
Real inductors have winding resistance, tolerance, saturation limits, self-heating and a self-resonant frequency. Always compare the Inductor Calculator results with the component datasheet and review inductor circuit fundamentals from All About Circuits. Keep expected peak current below the saturation and thermal ratings, and use measurement or circuit simulation when losses, waveform distortion or safety margins are important.
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Frequently asked questions
What is inductive reactance?
The opposition an ideal inductor presents to alternating current. It rises with frequency and inductance.
Does an inductor oppose DC?
At steady DC an ideal inductor has zero reactance, but a real winding has resistance and transient behavior.
What is the RL time constant?
L/R in seconds; it describes ideal current rise or decay.
Why does saturation matter?
Beyond saturation, inductance can fall sharply and circuit current may rise.