Acquire the necessary data. You will need the inductance, measured in Henries, and the AC frequency, measured in Hertz. The inductance is usually written on the inductor itself or may be referenced in a schematic. The frequency is usually notated in an electronic schematic.
Convert inductance as needed. Inductance is frequently expressed as micro-Henries, which represents 1,000,000 Henries. To convert to Henries, you would divide the number of micro-Henries by 1,000,000.
Calculate reactance, in ohms, by using the formula: Reactance = 2 * pi * Frequency * Inductance. Pi is simply a constant, measured as 3.14.