LC resonant frequency calculator
Work out the resonant frequency of an LC circuit (series or parallel) — or, working backwards, the L or C needed for a target frequency.
LC tank values
Resonant frequency
Resonant frequency (f)
f = 1 / (2π√(LC))
Inductor reactance (Xl)
Xl = 2πfL
Capacitor reactance (Xc)
Xc = 1 / (2πfC)
At resonance the two reactances are equal (here 100 Ω) — a quick sanity check on the result.
About the model
A capacitor and inductor wired in parallel or series form a resonant tank. At the resonant frequency the inductive and capacitive reactances cancel (Xl = Xc), so the tank either passes or blocks that frequency: series resonance is a low impedance, parallel resonance a high one. The frequency is set entirely by f = 1/(2π√(LC)).
Real parts add losses — the coil's series resistance and the capacitor's ESR damp the resonance and shift it slightly. For the parts themselves: RF inductors and capacitors in our catalog carry the ratings you need.
Browse related parts:
Frequently asked questions
How is the resonant frequency of an LC circuit calculated?
The calculator uses f = 1 ÷ (2π√(LC)) with inductance in henries and capacitance in farads. Its defaults of L = 100 µH and C = 10 nF give f = 1 ÷ (2π√(100×10⁻⁶ × 10×10⁻⁹)) ≈ 159.2 kHz.
How do you find the inductor for a target resonant frequency?
In reverse mode with the capacitance held fixed the tool solves L = 1 ÷ (4π²f²C). For a target of 159.155 kHz with C = 10 nF it returns L = 100 µH, and it re-checks the result by feeding the solved L back into f = 1 ÷ (2π√(LC)).
What does it mean that the inductor and capacitor reactances are equal at resonance?
At resonance the inductive reactance Xl = 2πfL and the capacitive reactance Xc = 1 ÷ (2πfC) are equal, so the tank either passes or blocks that frequency — series resonance is a low impedance, parallel resonance a high one. The tool prints both reactances as a sanity check on the result.
Does parasitic resistance change the resonant frequency?
The calculator assumes an ideal LC tank. Real parts add the coil's series resistance and the capacitor's ESR, which damp the resonance and shift the frequency slightly, so the printed value is an ideal approximation rather than the exact measured peak.
Ideal LC model; real components add parasitic resistance that dampens and slightly shifts the resonance. ICBOMS provides this tool for reference only.