Capacitor Reactance Calculator
Compute a capacitor's impedance (reactance) at a given frequency.
Formula
Xc = 1 / (2πfC)
Inputs
- Frequency (Hz)
- Capacitance (µF)
What it does
A capacitor opposes AC with a reactance that falls as frequency rises: Xc = 1 / (2πfC).
Where it's used
Choosing coupling and decoupling capacitors and designing filters.
How to use it
- Enter the frequency.
- Enter the capacitance in µF.
- Read the reactance in ohms.
The formula explained
- Xc
- capacitive reactance, in ohms
- f
- frequency, in hertz
- C
- capacitance (entered in µF)
Worked example
A 0.47 µF capacitor on 50 Hz mains.
Inputs:
- Frequency: 50 Hz
- Capacitance: 0.47 µF
The calculator gives:
- Result: 6.773 kΩ
Tips and common mistakes
- At DC the reactance is infinite — a capacitor blocks DC.
- Current through a capacitor leads the voltage by 90°, so an ideal capacitor uses no real power.
- Mains capacitors must be safety-rated (X2/Y2) types.
Questions people ask
How does reactance change with frequency?
It is inversely proportional: double the frequency and the reactance halves. The 0.47 µF capacitor that shows 6.77 kΩ at 50 Hz shows 3.39 kΩ at 100 Hz.
How much current flows through a capacitor on the mains?
I = V / X_C. On 230 V at 50 Hz, a 0.47 µF capacitor (6.77 kΩ) passes about 34 mA. Capacitive-dropper power supplies use this, but they are not isolated from the mains and are dangerous to touch.
Is reactance the same as impedance?
Not quite. A real capacitor also has a small series resistance (ESR) and inductance (ESL). Above its self-resonant frequency the inductance wins and the part behaves like an inductor, which matters for decoupling at high frequencies.
Related Reactive & RLC calculators
- Capacitors in Series
- Capacitors in Parallel
- Inductors in Series
- Inductors in Parallel
- RLC Resonant Frequency
- RLC Parallel Resonance
- RC Time Constant
Enter your values to get the result with the formula, substituted values and an explanation of each step.