Reactance is the opposition a capacitor or inductor presents to alternating current, measured in ohms. Unlike resistance it depends on frequency: capacitive reactance drops as frequency rises, inductive reactance climbs.

What is the capacitive reactance formula?

Xc = 1 / (2πfC), where f is frequency in hertz and C is capacitance in farads. A 1 µF capacitor at 1 kHz has Xc ≈ 159 Ω.

What is the inductive reactance formula?

XL = 2πfL, where f is frequency in hertz and L is inductance in henries. A 1 mH inductor at 1 kHz has XL ≈ 6.28 Ω.

How do I find the resonant frequency of an LC circuit?

f₀ = 1 / (2π√(LC)). At that frequency Xc and XL are equal and cancel, so a series LC looks like a short and a parallel LC like an open. A 1 mH / 1 µF pair resonates near 5.03 kHz.

Reactance & Resonance Calculator

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Capacitors and inductors oppose AC current with a frequency-dependent resistance called reactance. A capacitor's reactance Xc = 1 / (2πfC) falls as frequency rises, while an inductor's reactance XL = 2πfL grows with frequency. Where the two are equal, an LC circuit resonates at f₀ = 1 / (2π√(LC)) — the basis of tuned filters, oscillators and radio front-ends. This calculator does all three: pick a mode, enter the frequency and the component value with its unit, and read the reactance in ohms, or enter L and C to get the resonant frequency. Values accept the usual engineering units (pF to F, nH to H, Hz to GHz) and the output auto-scales to mΩ/Ω/kΩ/MΩ or Hz/kHz/MHz/GHz.

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Mode

Frequency

Capacitance

Reactance

159.1549 Ω

Formula: Xc = 1 / (2π × f × C)

Reactance is frequency-dependent: Xc falls as frequency rises, XL grows. At resonance Xc = XL and they cancel.

How to use

Pick a mode: capacitive reactance Xc, inductive reactance XL, or LC resonance.
Enter the frequency and the component value, each with its unit.
Read the reactance in ohms (or the resonant frequency) and the formula used.

Frequently asked questions

What is reactance?: Reactance is the opposition a capacitor or inductor presents to alternating current, measured in ohms. Unlike resistance it depends on frequency: capacitive reactance drops as frequency rises, inductive reactance climbs.
What is the capacitive reactance formula?: Xc = 1 / (2πfC), where f is frequency in hertz and C is capacitance in farads. A 1 µF capacitor at 1 kHz has Xc ≈ 159 Ω.
What is the inductive reactance formula?: XL = 2πfL, where f is frequency in hertz and L is inductance in henries. A 1 mH inductor at 1 kHz has XL ≈ 6.28 Ω.
How do I find the resonant frequency of an LC circuit?: f₀ = 1 / (2π√(LC)). At that frequency Xc and XL are equal and cancel, so a series LC looks like a short and a parallel LC like an open. A 1 mH / 1 µF pair resonates near 5.03 kHz.

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