Capacitive Reactance Calculator
Calculate capacitive reactance XC = 1/(2πfC) of a capacitor in AC circuits. Get angular frequency, susceptance, interactive charts, and formula breakdown — free online physics tool.
About This Calculator
The Capacitive Reactance Calculator helps you compute the opposition a capacitor offers to alternating current (AC) in an electrical circuit. Using the formula XC = 1/(2πfC), it calculates the capacitive reactance in ohms (Ω) based on the capacitance value and the AC frequency. This calculator is essential for electronics engineers, physics students, hobbyists, and anyone working with AC circuits, filters, or power supplies.
Capacitive reactance is inversely proportional to both frequency and capacitance — as frequency increases, the reactance decreases, and larger capacitors also reduce reactance. In DC circuits (0 Hz), a capacitor acts as an open circuit with infinite reactance. The calculator also provides the angular frequency (ω = 2πf) and the capacitive susceptance (BC = 1/XC), offering a complete picture of the circuit's frequency response.
The formula used is: XC = 1 / (2 × π × f × C) where f is the frequency in hertz and C is the capacitance in farads. For convenience, enter small capacitance values in scientific notation (e.g., 1e-6 for 1 microfarad). The output includes formatted results that automatically scale to kΩ or MΩ as needed.
Regional Notes
India and UK: Standard mains frequency is 50 Hz. Common motor-run capacitor values range from 1 µF to 50 µF. Ceiling fan capacitors typically use 1.5 µF to 3.5 µF values.
US and Americas: Standard mains frequency is 60 Hz. Air conditioner capacitor values commonly range from 5 µF to 80 µF. Audio crossover filters use much smaller values in the nF to µF range.
Frequently Asked Questions
What is capacitive reactance?
Capacitive reactance (XC) is the opposition a capacitor offers to alternating current (AC), measured in ohms (Ω). Unlike resistance which affects both DC and AC, reactance specifically opposes AC and varies with frequency. The formula is XC = 1/(2πfC), where f is frequency in Hz and C is capacitance in Farads.
How does frequency affect capacitive reactance?
Capacitive reactance is inversely proportional to frequency — as frequency increases, reactance decreases. At DC (0 Hz), a capacitor acts as an open circuit with infinite reactance. At very high frequencies, it acts nearly as a short circuit with near-zero reactance.
What is the difference between capacitive reactance and resistance?
Resistance opposes both DC and AC current and dissipates energy as heat. Capacitive reactance only opposes AC, stores and releases energy in an electric field, and varies with frequency. Resistance has a constant value regardless of frequency, while capacitive reactance decreases as frequency increases.
What is the unit of capacitive reactance?
Capacitive reactance is measured in ohms (Ω), the same unit as resistance. For typical circuit values, it ranges from milliohms (mΩ) to megaohms (MΩ), depending on the capacitance and frequency.
How do you calculate capacitive reactance?
Capacitive reactance is calculated using the formula XC = 1/(2πfC), where f is the frequency in hertz (Hz) and C is the capacitance in farads (F). You can also use XC = 1/(ωC) where ω = 2πf is the angular frequency in rad/s. For example, a 1 µF capacitor at 60 Hz has XC ≈ 2.65 kΩ.
What happens to capacitive reactance when capacitance increases?
Capacitive reactance is inversely proportional to capacitance — larger capacitance values result in lower reactance. This is because a larger capacitor can store more charge, allowing AC current to flow more easily through the circuit.
Is capacitive reactance positive or negative?
In impedance calculations, capacitive reactance is considered negative (XC = −1/(ωC)) because the voltage across a capacitor lags the current by 90 degrees. However, the magnitude of opposition is always a positive value expressed in ohms.
Can I share my calculation results?
Yes, the calculator saves your input values in the URL automatically, so you can copy the page URL to share your exact calculation with others. Simply click calculate and then share the URL.