Inductive Reactance Calculator

The Inductive Reactance Calculator works out the AC opposition of an inductor using the formula \( X_L = 2\pi f L \). Unlike most reactance calculators, this one lets you solve for reactance, frequency, or inductance in a single tool, auto-scales the answer into sensible engineering units, and shows why the number matters — with an animated voltage-current waveform and a reactance-versus-frequency curve.

What Is Inductive Reactance?

Inductive reactance (symbol \( X_L \), measured in ohms) is the opposition that an inductor presents to alternating current. An inductor resists changes in current by generating a back-EMF, so the faster the current alternates, the harder the inductor pushes back. Because it stores energy in a magnetic field and returns it each cycle rather than dissipating it as heat, reactance differs from ordinary resistance: it consumes reactive power, not real power.

Inductive Reactance Formula

Where \( X_L \) is the reactance in ohms (Ω), \( f \) is the frequency in hertz (Hz), and \( L \) is the inductance in henries (H). The term \( 2\pi f \) is the angular frequency \( \omega \), so the formula is often written \( X_L = \omega L \). Rearranging lets you solve for the other quantities:

Why Reactance Rises With Frequency

Reactance is directly proportional to frequency. Double the frequency and the reactance doubles; halve it and the reactance halves. This is the property that makes inductors so useful in filters and crossovers:

• At DC (f = 0): \( X_L = 0 \) Ω — the inductor acts like a plain wire (a short circuit).
• At low frequencies: low reactance — most of the AC passes through.
• At high frequencies: high reactance — the inductor blocks the signal, acting as a "choke".

This is exactly the opposite of a capacitor, whose reactance falls as frequency rises.

Voltage and Current Are 90° Out of Phase

In an ideal inductor, the current lags the voltage by 90 degrees (a quarter cycle). Voltage peaks first; current follows a quarter of a cycle later. A handy mnemonic is "ELI" — in an inductor (L), voltage (E) comes before current (I). This phase shift is why an ideal inductor consumes no real power: over a full cycle it returns as much energy to the source as it draws.

Inductive Reactance at Common Frequencies

The table below shows the reactance of a few typical inductors at everyday frequencies, to give you a feel for the scale.

What Uses Inductive Reactance?

How to Use This Calculator

1. Choose what to solve for: reactance \( X_L \), frequency \( f \), or inductance \( L \). The form shows only the fields you need.
2. Enter the known values: type the two known quantities and select their units (Hz/kHz/MHz/GHz, H/mH/µH/nH, Ω/kΩ/MΩ).
3. Add applied voltage (optional): enter an RMS voltage to also get the current and reactive power.
4. Click Calculate: review the result, the animated waveform, the frequency-response curve, and the step-by-step solution.

Frequently Asked Questions

What is inductive reactance?

Inductive reactance is the opposition an inductor presents to alternating current. It is measured in ohms and calculated with \( X_L = 2\pi f L \), where f is frequency in hertz and L is inductance in henries. Unlike resistance, reactance does not dissipate energy as heat; it stores and returns it each cycle.

What is the formula for inductive reactance?

The formula is \( X_L = 2\pi f L \). Reactance in ohms equals two pi times the frequency in hertz times the inductance in henries. Rearranged, frequency is \( f = X_L / (2\pi L) \) and inductance is \( L = X_L / (2\pi f) \).

Why does inductive reactance increase with frequency?

An inductor opposes changes in current. At higher frequencies the current changes direction more rapidly, so the inductor generates a larger opposing voltage. Because \( X_L \) is directly proportional to frequency, doubling the frequency doubles the reactance.

Does an inductor make current lead or lag voltage?

In an ideal inductor the current lags the voltage by 90 degrees. Voltage reaches its peak a quarter of a cycle before the current does. This phase relationship is why an inductor consumes reactive power rather than real power.

What is the inductive reactance of an inductor at DC?

At DC the frequency is zero, so \( X_L = 2\pi \times 0 \times L = 0 \) ohms. An ideal inductor behaves like a plain wire, or short circuit, for direct current, which is why inductors block AC while passing DC.

How do I calculate current through an inductor?

For a purely inductive AC circuit, the RMS current is \( I = V / X_L \), where V is the RMS voltage and \( X_L \) is the inductive reactance in ohms. The reactive power is \( Q = V \times I \), expressed in VAR.

Additional Resources

• Electrical Reactance - Wikipedia
• Inductor - Wikipedia