Capacitive Reactance Calculator

About this calculator

Capacitive reactance measures the opposition a capacitor presents to alternating current: Xc = 1 / (2πfC), where f is frequency and C is capacitance. Unlike a resistor, a capacitor's opposition to current isn't constant — it falls as frequency rises (a capacitor passes high frequencies more easily) and rises toward infinity as frequency approaches zero (a capacitor blocks DC entirely).

Electrical and electronics engineers use this relationship to design filters — a capacitor in the right configuration builds a low-pass or high-pass filter purely from this frequency-dependent behavior — as well as for impedance matching and power-factor correction in AC circuits. Students studying AC circuit analysis and hobbyist circuit designers use this calculator to check reactance at a chosen frequency before building or simulating a circuit.