📻 LC Resonant Frequency Calculator
Enter an inductance and capacitance to get the LC circuit's resonant frequency and its characteristic impedance.
Resonant frequency
1.592 MHz
Characteristic impedance √(L/C)
1000 Ω
An LC tank circuit resonates where the inductive and capacitive reactances cancel, at fₒ = 1 ÷ (2π·√(L·C)). The characteristic impedance √(L/C) is the reactance of each element at resonance. This is the tuning frequency of filters, oscillators and radio front-ends; a real circuit's sharpness (Q) also depends on its resistance. 🔒 In your browser.
How the lc resonant frequency calculator works
An inductor and capacitor together form a resonant "tank": the inductor's reactance rises with frequency while the capacitor's falls, and at one frequency they're equal and cancel. That resonant frequency is fₒ = 1 ÷ (2π·√(L·C)). The tool also gives the characteristic impedance √(L/C) — the reactance of each element at resonance — which sets the impedance level of the tuned circuit. Pick any henry and farad units; they're converted automatically.
This is the ideal (lossless) resonance. A real circuit's resistance sets its Q (sharpness) and slightly shifts a series-vs-parallel resonance, but the frequency formula is the standard starting point for tuning filters, oscillators and antenna matching. To halve the frequency, quadruple either L or C (frequency scales with 1/√).
Frequently asked questions
How do I calculate LC resonant frequency?
fₒ = 1 ÷ (2π·√(L·C)), with L in henries and C in farads. For L = 100 µH and C = 100 pF that's about 1.59 MHz. Larger L or C gives a lower frequency.
What is a resonant (tank) circuit?
An inductor and capacitor connected so energy sloshes between the magnetic field of the coil and the electric field of the capacitor. It naturally oscillates at its resonant frequency — the basis of radio tuning, oscillators and filters.
What happens at resonance?
The inductive and capacitive reactances are equal and opposite, so they cancel. A series LC then looks like a very low impedance (a short) and a parallel LC like a very high impedance (an open), which is what makes them select one frequency.
How do I change the resonant frequency?
Adjust L or C. Because frequency depends on 1/√(L·C), quadrupling either value halves the frequency; doubling both drops it to about 71%. Variable capacitors or tunable inductors are how radios sweep across a band.
What is the characteristic impedance √(L/C)?
The magnitude of each element's reactance at resonance, which sets the tank's impedance level. Together with the circuit's resistance it determines the quality factor Q and thus how sharp the resonance is.
Does the resistance matter for the frequency?
For the ideal formula, no — resonance depends only on L and C. Resistance mainly sets the Q (bandwidth/sharpness) and causes a small shift in lossy circuits, but fₒ = 1 ÷ (2π·√(L·C)) is the standard design value.