Inductive Reactance Calculator

Inductive reactance is the opposition an inductor offers to alternating current (AC), measured in ohms (Ω). The formula is XL = 2πfL, with f frequency in hertz and L inductance in henries. Unlike a resistor, inductive reactance depends on frequency: the higher the frequency, the greater the opposition.

Because an inductor opposes changes in current. The faster current reverses direction (the higher the frequency), the larger the opposing induced voltage the coil generates, so opposition rises linearly: doubling frequency doubles XL. This is why inductors are used as chokes that pass DC but block high-frequency signals.

Resistance (R) turns electrical energy into heat and stays constant at all frequencies. Inductive reactance (XL) stores energy in the magnetic field then returns it to the circuit each cycle, so it wastes no power, and its value varies with frequency. On DC, a resistor still impedes current while an ideal inductor behaves like a plain wire (XL = 0).

At DC, XL = 2π × 0 × L = 0 Ω, so an ideal inductor behaves like a short circuit for settled direct current. Honestly: a real inductor still has small wire resistance (DCR), so on DC it behaves like a small resistor, not a perfect short.

Use the 3-way solver in the first tab: pick the target variable, then enter the other two. For example XL = 31.4159 Ω and f = 50 Hz give L = 100 mH. The inverse formulas are f = XL / (2πL) and L = XL / (2πf).

In an ideal inductor, current lags 90° behind voltage, equivalently: voltage leads current by +90°. Its impedance is written Z = j·XL with a +90° phase angle. This is the opposite of a capacitor, whose current leads voltage by 90°.

Because at high frequencies their reactance is large so they choke unwanted AC signals, while DC and low frequencies pass easily. An example is the choke in a power supply that damps high-frequency ripple without wasting power like a resistor.

No. This calculator models an ideal inductor: only reactance XL = 2πfL with no series resistance (ESR/DCR). A real inductor has small wire resistance adding slight power loss and shifting the phase angle slightly below +90°. For precision analysis, add DCR in series with the XL result.

XL determines LC filter behavior, speaker crossover points, RF impedance matching, and choke selection. Anchor example: a 100 mH inductor has XL = 31.4159 Ω on 50 Hz mains and 37.6991 Ω on 60 Hz, so AC leakage current passing through is far smaller than at audio frequencies.

1 H = 1,000 mH = 1,000,000 µH = 1,000,000,000 nH. This calculator accepts all of these units along with Hz, kHz, and MHz for frequency, and Ω, kΩ, and mΩ for reactance results, so no manual conversion is needed.