Capacitive Reactance Calculator

The formula

Capacitive reactance is given by:

Xc = 1 / (2 × π × f × C)

where f is the frequency in hertz (Hz) and C is the capacitance in farads (F). The result Xc is in ohms (Ω). Reactance is inversely proportional to both frequency and capacitance: double the frequency and Xc halves; double the capacitance and Xc halves too. The angular form is Xc = 1 / (ω × C), where ω = 2 × π × f.

Because the input here is in microfarads, the tool first converts it: C (F) = C (µF) × 10⁻⁶.

Worked example

Take f = 60 Hz and C = 100 µF (= 100 × 10⁻⁶ F):

2 × π × f = 2 × π × 60 ≈ 376.99
Xc = 1 / (376.99 × 100 × 10⁻⁶)
   = 1 / 0.037699
   ≈ 26.53 Ω

So a 100 µF capacitor presents about 26.5 Ω to a 60 Hz signal — small enough to be a useful bypass at mains frequency.

Reactance at common values

Pitfalls to avoid

• Units matter. This tool expects hertz and microfarads. 1 nF = 0.001 µF and 1000 pF = 0.001 µF; 1 mF = 1000 µF. Mixing prefixes shifts Xc by orders of magnitude.
• Reactance is not resistance. Xc stores and returns energy rather than dissipating it, so it adds to resistance vectorially: total impedance is Z = √(R² + Xc²), not R + Xc.
• At DC (f → 0) the reactance is infinite. A capacitor blocks direct current; this calculator returns 0 for a zero frequency or zero capacitance as a safe guard, since the ideal value would be undefined.
• Real caps have ESR and leakage. The ideal Xc is an excellent estimate, but equivalent series resistance and a finite self-resonant frequency matter at high frequencies, so treat the figure as a starting point.