wikiHow Impedance Calculator Impedance is a measure of the opposition that a circuit presents to the flow of alternating current (AC). It is measured in ohms (Ω) and is calculated using the following formula: Z = √(R² + X²) where Z is the impedance in ohms, R is the resistance in ohms, and X is the reactance in ohms. Reactance is a measure of the opposition that a circuit presents to the flow of AC due to capacitance or inductance, and is calculated using the following formulas: For capacitive reactance: Xc = 1/(2πfC) where Xc is the capacitive reactance in ohms, f is the frequency in hertz (Hz), and C is the capacitance in farads (F). For inductive reactance: Xl = 2πfL where Xl is the inductive reactance in ohms, f is the frequency in hertz (Hz), and L is the inductance in henries (H). Once you have calculated the values of R and X, you can substitute them into the formula for impedance to calculate Z. Page