Capacitive Reactance Calculator

Capacitive reactance (XC) is the opposition a capacitor presents to alternating current (AC). Unlike resistance, which dissipates energy as heat, reactance stores and releases energy in the electric field of the capacitor. It is measured in ohms (Ω) and decreases as frequency or capacitance increases.

The capacitive reactance formula is XC = 1 / (2 × π × f × C), where f is the frequency in hertz and C is the capacitance in farads. It can also be written as XC = 1 / (ω × C), where ω = 2πf is the angular frequency in radians per second.

Capacitive reactance (XC) is measured in ohms (Ω), the same unit as electrical resistance. This makes sense because reactance and resistance both describe opposition to current flow, and they combine in the same impedance equation Z = R ± j × X.

Using XC = 1 / (2 × π × f × C): XC = 1 / (2 × π × 60 × 15 × 10⁻⁹) ≈ 176,839 Ω (approximately 176.8 kΩ). You can verify this instantly using the calculator above by entering 15 nF and 60 Hz.

At higher frequencies, the AC signal reverses direction more rapidly, so the capacitor has less time to fully charge before the current reverses. This means the capacitor presents less opposition to current flow at high frequencies. Conversely, at very low frequencies (approaching DC), the capacitor blocks current almost entirely, resulting in very high reactance.

Both resistance (R) and reactance (X) are measured in ohms and oppose current flow, but they behave differently. Resistance dissipates energy as heat and is constant regardless of frequency. Reactance stores energy (in electric or magnetic fields) and is frequency-dependent. Together they form impedance: Z = R + jX.

In a DC circuit, the frequency is zero (f = 0), which means the capacitive reactance XC = 1/(2πfC) becomes infinite. This means an ideal capacitor completely blocks DC current once it is fully charged — it acts as an open circuit at steady-state DC.

Admittance (BC) is the reciprocal of reactance: BC = 1 / XC = 2 × π × f × C. It is measured in siemens (S) and represents how easily AC current can flow through the capacitor. A higher admittance means less opposition to current flow.