How this calculator works
An ideal capacitor opposes sinusoidal current by a reactance whose magnitude decreases as frequency or capacitance increases. Its complex impedance is negative imaginary, so this positive magnitude does not describe resistance or heat loss. Hertz counts cycles per second; angular frequency counts radians per second. Zero frequency represents an ideal open circuit and has no finite reactance.
Formula
Xc = 1/(2 pi f C) = 1/(omega C); omega = 2 pi f. C = 1/(2 pi f Xc), f = 1/(2 pi C Xc).
Worked example
A 1 microfarad capacitor at 1000 Hz has reactance 159.15494 ohm. With C = 0.01 F and omega = 100 rad/s, reactance is exactly 1 ohm.
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Frequently asked questions
Is this a negative resistance?
No. The magnitude is positive; the complex impedance is -jXc and describes a 90-degree phase shift.
Can I use DC?
At DC an ideal capacitor has unbounded reactance after charging, so a positive frequency is required here.
Does this include equivalent series resistance?
No. ESR, leakage and lead inductance require a nonideal capacitor model.