Reactance & Resonance Calculator
Find capacitive reactance (Xc), inductive reactance (XL), or the LC resonant frequency, with pF–F, nH–H and Hz–GHz unit pickers.
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.
About this tool
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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.
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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