Find a capacitor’s reactance — its opposition to alternating current — from the signal frequency and the capacitor’s value.
How it works
The formula is Xc = 1 ÷ (2π × f × C). A 100 µF capacitor at 60 Hz has a reactance of about 26.5 ohms. Reactance falls as frequency rises — a capacitor passes high frequencies more easily than low ones.
What this does not include
This calculates ideal capacitive reactance only. It doesn’t account for a real capacitor’s equivalent series resistance or other non-ideal behavior that shows up at very high frequencies.
How to use this calculator
- Enter the frequency in hertz.
- Enter the capacitance in farads.
A worked example
A 100 µF capacitor at 60 Hz: reactance = 1/(2πfC) = 26.525824 Ω.
A 1 µF capacitor at 1,000 Hz: reactance = 159.154943 Ω.
What the variables mean
| Variable | Meaning |
|---|---|
| Frequency | AC signal frequency, in hertz |
| Capacitance | Capacitor value, in farads |
Edge cases worth knowing
Capacitive reactance falls as frequency rises — the opposite of inductive reactance, which rises with frequency. This is why capacitors pass high-frequency signals more easily than low-frequency ones.
Zero frequency makes reactance infinite — a capacitor blocks DC current entirely, which is exactly why the calculator declines to show a finite result at zero frequency.
Why does reactance decrease as frequency increases?
A capacitor stores and releases charge each cycle; at higher frequencies it has less time per cycle to charge up, so it presents less opposition to the current flowing through it.
How is capacitive reactance different from resistance?
Resistance dissipates energy as heat; reactance stores and releases energy without dissipating it, and it depends on frequency, while resistance (for an ideal resistor) does not.
What’s a typical capacitance value in microfarads vs. farads?
Most everyday capacitors are rated in microfarads (µF) or smaller, since a full farad is an enormous amount of capacitance — enter capacitance in farads here, converting from µF by dividing by 1,000,000.
