Inductive Reactance Calculator

Inductive reactance (XL) is how strongly an inductor, or coil, opposes alternating current, in ohms. It rises with the frequency and the inductance: a coil lets low frequencies through and holds back high ones. To direct current, at 0 Hz, an ideal coil is a plain wire.

XL = 2 * π * f * L

where f is the frequency in hertz and L the inductance in henries. Enter any two of the three, and the calculator finds the third:

• L = XL / (2 * π * f)
• f = XL / (2 * π * L)

Examples

1. A 10 mH coil at 1 kHz: 10 mH is 0.01 H.

   XL = 2 * π * 1000 * 0.01 = 62.83 Ω

2. The inductance for 100 Ω at 50 Hz:

   L = 100 / (2 * π * 50) = 0.3183 H

3. The frequency where 1 mH has 1 kΩ:

   f = 1000 / (2 * π * 0.001) = 159,200 Hz

Each field has its own unit menu, so values can be entered in mH, µH, kHz or kΩ directly.

Frequently asked questions

What is the difference between reactance and impedance?

Reactance is the opposition of the coil alone. Real coils also have resistance (R), and the two combine into the impedance: Z = √(R² + XL²). In an inductor, the current lags the voltage by 90°.

How is it related to capacitive reactance?

A capacitor does the opposite, with Xc = 1 / (2 * π * f * C) falling with frequency. Where the two are equal, a circuit resonates. See the Capacitive Reactance Calculator and the Resonant Frequency Calculator.