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Capacitive Reactance Calculator (Xc)

Compute opposition to AC current flow in capacitors. Supports Hz/kHz/MHz and pF/nF/µF with reverse calculation logic for circuit design.

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About

In AC circuits, capacitors resist the flow of current not through resistance, but through reactance ($X_c$). Unlike a resistor, this opposition is frequency-dependent. As frequency increases, reactance decreases, allowing more current to pass. This property makes capacitors essential for filtering, blocking DC components, and tuning resonant circuits.

This calculator determines the reactance in Ohms based on signal frequency and capacitance. Precise calculation is critical in RF design, audio crossover networks, and power supply decoupling. It accounts for standard unit prefixes to streamline the workflow for engineers and hobbyists.

reactance calculator electronics tool impedance capacitor calculator ac circuits

Formulas

The reactance of a capacitor is inversely proportional to both frequency (f) and capacitance (C).

Xc = 12 π f C

Where:

  • π ≈ 3.14159
  • f is frequency in Hertz (Hz)
  • C is capacitance in Farads (F)

Reference Data

FrequencyCapacitanceReactance ($X_c$)Application
50 Hz10 μF318.3 ΩPower Supply smoothing
1 kHz1 μF159.1 ΩAudio High-Pass Filter
100 kHz100 nF15.9 ΩSwitching Regulator Decoupling
10 MHz10 pF1591 ΩRF Oscillator Tank

Frequently Asked Questions

At 0 Hz (DC), the denominator becomes zero, mathematically resulting in infinite reactance. In practice, this means the capacitor acts as an open circuit, blocking DC current entirely once charged.
Resistance dissipates energy as heat. Reactance stores energy (in an electric field) and returns it to the circuit. While both are measured in Ohms, they behave differently regarding power consumption and phase shift.
At very high frequencies (often >100 MHz for larger caps), the physical leads and construction of the capacitor create a small inductance. This can cause the capacitor to behave like an inductor, increasing impedance instead of decreasing it.