Electronics · AC
Capacitive reactance calculator.
Enter a frequency and a capacitance to get the capacitor’s opposition to AC, in ohms.
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Capacitive reactance formula
Capacitive reactance is XC = 1 ÷ (2π × f × C), in ohms when f is in hertz and C is in farads. It falls as frequency or capacitance rises, which is why a capacitor passes high frequencies and blocks low ones. At DC (0 Hz) it is effectively infinite.
Worked example. 1 µF at 1 kHz: XC = 1 ÷ (2π × 1,000 × 0.000001) = 159.2 Ω.
Some texts write capacitive reactance as a negative number (−1/ωC) so it sits on the opposite side of zero from inductive reactance. This page shows the positive magnitude. Reactance is not resistance: it stores and returns energy rather than dissipating it.
Frequently asked questions
What is the formula for capacitive reactance?
XC = 1 ÷ (2πfC). With f in Hz and C in farads, XC is in ohms.
What is the reactance of 1 µF at 1 kHz?
About 159.2 ohms.
Why does reactance drop as frequency rises?
A higher frequency moves charge on and off the plates faster, so the capacitor opposes the current less.
What is the reactance at 0 Hz?
It is infinite: an ideal capacitor blocks steady DC.
Is capacitive reactance the same as resistance?
No. Both are measured in ohms, but reactance does not dissipate power and depends on frequency.
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Scope and safety
Low-voltage hobby and study use only. Results are ideal-component arithmetic from the formulas shown, not an engineering design or professional advice. Real parts vary with tolerance, temperature and age, so check the datasheet for every part. Never work on mains-powered circuits from a calculator result, and discharge large capacitors safely before handling.