Reactance Calculator
Inductive and capacitive reactance and LC resonant frequency.
About this tool
Enter a frequency, an inductance and a capacitance, choosing units from nH to H and pF to mF. The tool shows each reactance, the resonant frequency and the net reactance in series and parallel.
Reactance and resonance
Inductors and capacitors oppose alternating current with reactance, measured in ohms but depending on frequency. Inductive reactance rises with frequency, X_L = 2ฯfL; capacitive reactance falls, X_C = 1 รท (2ฯfC). At 1 kHz, a 10 mH inductor has 62.8 ฮฉ of reactance and a 1 ยตF capacitor 159 ฮฉ. When the two are equal the circuit resonates, at fโ = 1 รท (2ฯโ(LC)), which is about 1.59 kHz for this pair. In series, the reactances cancel at resonance, leaving only resistance, which is how series LC filters pass one frequency. In parallel, the net reactance rises towards infinity at resonance, the basis of tank circuits in radio tuners and oscillators. The tool also gives โ(L/C), the reactance of each part at resonance. Honest limits: these are ideal components. Real inductors have winding resistance and self-capacitance, capacitors have ESR and ESL, and at radio frequencies stray capacitance and inductance can dominate. The RC filter calculator and the antenna length calculator are related.
Frequently asked questions
What is the formula for inductive reactance?
X_L = 2ฯ ร frequency ร inductance.
What is the formula for capacitive reactance?
X_C = 1 รท (2ฯ ร frequency ร capacitance).
How do I calculate LC resonant frequency?
fโ = 1 รท (2ฯโ(LC)). 10 mH with 1 ยตF resonates at about 1.59 kHz.
What happens at resonance?
X_L equals X_C. In series the reactances cancel; in parallel the impedance becomes very high.
Is my data sent anywhere?
No. Everything is calculated in your browser, and nothing is stored or sent.