Capacitive Reactance
Frequency & capacitance
Xc = 1/(2πfC). Enter f and C; the reactance, admittance and phase appear live.
Reactance
How to use this calculator
Capacitive reactance is the opposition a capacitor offers to AC, and it decreases as frequency rises: Xc = 1 / (2πfC). Enter the frequency and capacitance and the reactance (in Ω, kΩ or MΩ) appears live, along with the susceptance/admittance B = 2πfC and the −90° phase (current leads voltage). At DC (f = 0) a capacitor is an open circuit; at very high f it behaves like a short.
What it means in a real circuit
Xc is central to coupling, bypass, and filter design. A bypass capacitor's effectiveness depends on Xc being small at the signal frequency; a coupling cap's Xc must be small enough not to load the previous stage. Computing Xc tells you whether a given cap is "big enough" at the frequency you care about — a daily check in both audio and RF work.