Inductive Reactance Calculator
Enter an inductance and a frequency to get the inductive reactance in ohms — and see why a coil opposes alternating current more strongly as the frequency rises.
Reactance in one step
Enter the inductance in henries and the frequency in hertz and the calculator returns the inductive reactance (Xl = 2π·f·L) in ohms.
Use SI units
Inductance in henries and frequency in hertz give reactance in ohms — divide millihenries by 1000 to get henries before you start.
What is inductive reactance?
A coil's opposition to AC
This inductive reactance calculator finds how strongly a coil resists alternating current. Inductive reactance is the opposition an inductor presents to a changing current, measured in ohms, and it depends on two things: the inductance of the coil and the frequency of the signal. The higher either one is, the more the coil opposes the current. It is the value behind crossover networks in speakers, the behaviour of transformers, and any filter that needs to block high frequencies while letting low ones pass.
Enter an inductance in henries and a frequency in hertz to get the inductive reactance in ohms instantly.
Inductive reactance is two times pi, multiplied by the frequency, multiplied by the inductance.
Xl = 2π × f × LBoth the frequency and the inductance enter the formula to the first power, so the reactance rises in direct proportion to each. Double the frequency and the reactance doubles; double the inductance and it doubles too. Use henries and hertz and the reactance comes back in ohms, the same unit as ordinary resistance.
Suppose a 0.1 H coil is connected to a 60 Hz mains supply.
Find 2π
2 × π = 6.283185 — the constant that turns frequency into angular frequency.
Multiply by the frequency
6.283185 × 60 = 376.991118 — the angular frequency in radians per second.
Multiply by the inductance
376.991118 × 0.1 = 37.699112 Ω — the inductive reactance of the coil.
The reactance in ohms tells you how much the coil opposes the alternating current at that frequency, just as a resistor's value tells you how much it opposes a direct current. The key difference is that reactance changes with frequency: the 0.1 H coil above shows 37.7 Ω at 60 Hz, but at 600 Hz it would show ten times as much, about 377 Ω, and at very high frequencies it behaves almost like an open circuit. This frequency dependence is exactly what makes inductors useful in filters and crossovers — they pass low frequencies easily and choke off high ones. A reactance near zero means the coil barely affects the signal; a large reactance means it dominates the circuit. To find the total opposition when a resistor is also present, you combine resistance and reactance as impedance rather than adding them directly, because the two are 90 degrees out of phase.
The formula is exact, but a couple of practical points are worth keeping in mind.
Ideal inductor and consistent units
This calculator gives the reactance of an ideal inductor. A real coil also has some winding resistance and self-capacitance, so its measured impedance differs slightly, especially at very high frequencies. Keep your units consistent — henries for inductance and hertz for frequency — or the ohms will be wrong: convert millihenries to henries by dividing by 1000 before you enter the value.