Inductive Reactance Calculator

Inductive reactance describes how strongly an inductor opposes alternating current. Unlike ordinary resistance, which dissipates electrical energy as heat, ideal inductive reactance temporarily stores energy in a magnetic field and returns it to the circuit. Its magnitude is XL = 2 pi f L, where frequency f is measured in hertz and inductance L is measured in henries. The result is measured in ohms. Because frequency appears directly in the formula, doubling frequency doubles reactance. The same is true for inductance. A practical coil also has winding resistance. This calculator therefore accepts an optional series resistance and combines it with reactance to find the magnitude of total impedance. Resistance and inductive reactance act along perpendicular axes in an impedance diagram, so their magnitudes are combined with the Pythagorean relationship. The phase angle is the arctangent of reactance divided by resistance. An ideal inductor has a 90-degree phase angle, while a resistance-dominated circuit has an angle closer to zero. Engineers use inductive reactance when selecting chokes, designing RL filters, estimating transformer behavior, and analyzing motors or solenoids on AC supplies. A coil that passes low-frequency current may substantially limit high-frequency current. This frequency dependence is useful in filters and noise suppression, but it can also produce unexpected voltage drops if omitted from a design calculation. Radio systems use the same principle for tuning and impedance matching. Audio crossover networks likewise rely on a coil's increasing opposition as signal frequency rises. Use RMS frequency-domain values when applying the result to steady sinusoidal circuits. Real inductors also have parasitic capacitance, core loss, saturation, and frequency-dependent winding resistance. Those effects can make measured impedance differ from this ideal series-RL model, especially near self-resonance or at high current. Check the component data sheet when precision, temperature rise, or safety margins matter. For ordinary low-frequency analysis, the formulas here provide a fast and transparent estimate of reactance, impedance, and current-voltage phase.