An opposition to the flow of alternating current or changing direct current, caused by inductance in the circuit. Inductive reactance, whose abbreviation is XL, is measured in ohms, and it decreases the amount of current flowing in a circuit. Resistance is also measured in ohms, and it too decreases the current, but resistance uses power and produces heat, while inductive reactance does not.

Inductive reactance is caused by the generation of an induced voltage whose polarity is opposite to that of the voltage causing it. The induced voltage opposes some of the applied voltage, and because there is less voltage available to force current through the circuit, less current flows. Inductive reactance increases as both the frequency of the alternating current and the inductance of the circuit increase. The formula for inductive reactance is: