Resonant Frequency LC Calculator
Calculate resonant frequency of LC circuits from inductance and capacitance values with step-by-step formulas.
What Is LC Resonant Frequency?
An inductor and capacitor store energy in magnetic and electric fields. When connected together, they exchange energy and oscillate at a natural frequency called the resonant frequency. LC tanks appear in radio tuners, filters, oscillators, and impedance-matching networks.
Resonant Frequency Formula
For an ideal parallel or series LC pair, resonant frequency is:
$$f = \frac{1}{2\pi\sqrt{LC}}$$Use inductance \(L\) in henries and capacitance \(C\) in farads to get \(f\) in hertz. Angular frequency is \(\omega = 2\pi f\).
Practical Unit Conversions
Circuit values are often given in microhenries and nanofarads. Convert to SI units before using the formula: \(10\,\mu\mathrm{H} = 10 \times 10^{-6}\,\mathrm{H}\) and \(100\,\mathrm{nF} = 100 \times 10^{-9}\,\mathrm{F}\). Real coils and capacitors also have parasitic resistance and lead inductance, so measured resonance may differ slightly from the ideal value.
Related tools: LC Filter Calculator, Frequency Bandwidth Calculator, and Capacitor Design Calculator.
Frequently Asked Questions
What units should I use for L and C?
Enter any common unit in the calculator. Internally, values are converted to henries and farads before applying \(f = 1/(2\pi\sqrt{LC})\).
Does series or parallel connection change the resonant frequency?
For an ideal LC pair, the resonant frequency formula is the same. What changes is impedance behavior: a parallel tank is high impedance at resonance, while a series tank is low impedance.
What is angular frequency?
Angular frequency \(\omega = 2\pi f\) is measured in radians per second. It appears in phasor analysis and differential equations for LC circuits.
How do I double the resonant frequency?
Either divide both L and C by 4, or divide only L or only C by 4, because frequency scales as \(1/\sqrt{LC}\).
Why is my measured frequency different from the calculated value?
Component tolerances, stray capacitance, wire inductance, and losses in real inductors shift the observed resonance away from the ideal formula.
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