Engineering
Capacitive Reactance Calculator
Calculate capacitive reactance from capacitance and frequency, or solve for capacitance or frequency. Includes impedance form, current from AC voltage, and phase behavior for a pure capacitor.
Capacitive reactance formula
Capacitive reactance is the opposition a capacitor presents to AC current. It falls as frequency rises and also falls as capacitance increases.
Xc = 1 ÷ (2πfC)
C = 1 ÷ (2πfXc)
f = 1 ÷ (2πCXc)
Pure capacitor impedance:
Zc = −jXc
Worked example
C = 1 µF
f = 1,000 Hz
Xc = 1 ÷ (2π × 1000 × 1e−6)
Xc ≈ 159.15 Ω
At higher frequency, the same capacitor has lower reactance. At lower frequency, it has higher reactance. That is why capacitors pass high-frequency signals more easily than low-frequency signals.
Trusted references
For deeper AC circuit background, use non-competitor educational references such as All About Circuits – AC capacitor circuits and All About Circuits – R, L, and C impedance.
Common questions
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Capacitive reactance is the opposition a capacitor presents to alternating current. It is measured in ohms.
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The formula is Xc = 1 ÷ (2πfC), where f is frequency in hertz and C is capacitance in farads.
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No. Capacitive reactance decreases as frequency increases.
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The impedance of an ideal capacitor is Zc = −jXc, where the negative imaginary sign represents the phase shift.
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For a sinusoidal RMS voltage, use I = V ÷ Xc for the ideal capacitive current magnitude.
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At zero frequency, capacitive reactance approaches infinity, so an ideal capacitor blocks steady DC after charging.
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It gives the ideal reactance. Real capacitors also have ESR, ESL, leakage, voltage limits, tolerance, and self-resonance.
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The formula uses farads, but this calculator accepts pF, nF, µF, mF, and F and converts automatically.