Inductor Calculator for Energy, Reactance, and Resonance
The inductor calculator is an all-in-one tool for analyzing how inductors behave in DC and AC circuits. Work out the energy stored in a coil, the inductive reactance at a given frequency, the total inductance of components in series or parallel, and the resonant frequency of an LC circuit.
Every tab shows real-time results with a full formula breakdown, so you see exactly how each value is derived. It is built for electronics students learning AC theory, hobbyists designing crossovers, filters, and power supplies, and engineers working on RF, SMPS, and LC tank circuits.
How to Use the Inductor Calculator
Basic — stored energy
On the Basic tab, enter the inductance (L) and current (I), each with its own unit. The calculator instantly shows the energy stored in the magnetic field using E = ½LI², with every substitution step.
Impedance — inductive reactance
On the Impedance tab, enter inductance and frequency to get the inductive reactance XL = 2πfL and a frequency response chart. Add a voltage to also see the resulting AC current.
Series & Parallel — total inductance
On the Series & Parallel tab, pick a mode, enter at least 2 inductors, and use Add Inductor for more (up to 10). The total inductance updates live with the combination formula.
Resonant — LC frequency & Q
On the Resonant tab, enter inductance and capacitance to find the resonant frequency f₀ = 1/(2π√LC). Add an optional resistance to also calculate the quality factor (Q) and bandwidth.
Features
Stored Energy
Compute the energy held in an inductor's magnetic field with E = ½LI², shown with SI-prefixed output and step-by-step substitution.
Inductive Reactance
Calculate XL = 2πfL for any inductance and frequency, with the full formula laid out line by line.
Frequency Response Chart
An interactive chart visualizes how reactance changes across the frequency range, with a marker on your current operating point.
AC Current
Add a voltage on the Impedance tab to derive the AC current through the inductor as I = V / XL.
Series & Parallel
Combine 2 to 10 inductors. Series sums values directly; parallel uses the reciprocal formula, with each inductor on its own unit.
LC Resonant Frequency
Find f₀ = 1/(2π√LC) for an LC circuit, plus the reactance at resonance where XL = XC.
Quality Factor & Bandwidth
Add a resistance on the Resonant tab to unlock the quality factor Q = (1/R)√(L/C) and the resulting bandwidth.
SI Prefix Support
Inputs and results use proper SI prefixes — nH to H, µA to A, Hz to MHz, pF to F, and mΩ to MΩ — for clean, readable numbers.
Adjustable Precision
Set decimal precision from 2 to 6 digits to match the accuracy you need for any calculation.
Quick Examples
Load real-world cases like a DC motor, SMPS choke, audio crossover, RF choke, and AM/FM radio tuning to populate inputs instantly.
Frequently Asked Questions
How do you calculate the impedance of an inductor?
For an ideal inductor in an AC circuit, the impedance equals its inductive reactance, XL = 2πfL, where f is the frequency in hertz and L is the inductance in henries. Enter L and f on the Impedance tab and the calculator returns XL in ohms. A pure inductor has zero resistance, so this reactance is what opposes the AC current.
What is the formula for inductive reactance?
Inductive reactance is XL = 2πfL. It is the opposition an inductor presents to alternating current and rises linearly with both frequency and inductance. Unlike resistance, reactance only affects AC signals, which is why the same coil that blocks high-frequency current can pass DC almost freely.
How much energy is stored in an inductor?
The energy stored in an inductor's magnetic field is E = ½LI², with L in henries and I in amperes giving energy in joules. On the Basic tab, enter the inductance and current and the result appears instantly with an SI-prefixed value (nJ, µJ, mJ, J) and the full substitution shown line by line.
How do you combine inductors in series and parallel?
In series, inductances add directly: Ltotal = L1 + L2 + …, giving a higher total. In parallel, the reciprocals add: 1/Ltotal = 1/L1 + 1/L2 + …, giving a lower total. This is the opposite of how capacitors combine. The Series & Parallel tab handles 2 to 10 inductors and recomputes as you type.
What is the resonant frequency of an LC circuit?
The resonant frequency is f₀ = 1/(2π√LC), the frequency at which the inductive reactance equals the capacitive reactance (XL = XC). At resonance, a series LC circuit reaches minimum impedance and a parallel LC circuit reaches maximum impedance, while energy oscillates between the coil's magnetic field and the capacitor's electric field.
What does the quality factor (Q) represent?
The quality factor Q measures how sharp the resonance peak is — a higher Q means a narrower bandwidth and more selective filtering. For an LC circuit with series resistance R, Q = (1/R)√(L/C), and the bandwidth follows as f₀/Q. Enter an optional resistance on the Resonant tab to see both values.
How does inductor impedance change with frequency?
Because XL = 2πfL, an inductor's reactance is directly proportional to frequency: double the frequency and you double the reactance. The frequency response chart on the Impedance tab plots this relationship and marks your current operating point so you can see the trend at a glance.
Is my data stored or sent to a server?
No. Every calculation is performed locally in your browser with JavaScript. Nothing you enter is uploaded, stored, or tracked.
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