Electronics · Resonance
LC resonant frequency calculator.
Enter any two of inductance, capacitance and frequency. Leave the one you want solved blank.
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LC resonant frequency formula
An ideal LC circuit resonates at f₀ = 1 ÷ (2π√(L × C)), in hertz when L is in henries and C is in farads. At that frequency the inductive and capacitive reactances are equal. Rearranged, C = 1 ÷ ((2πf)² × L) and L = 1 ÷ ((2πf)² × C).
Worked example. 1 mH and 1 µF: √(0.001 × 0.000001) = 3.162 × 10⁻⁵, so f₀ = 1 ÷ (2π × 3.162 × 10⁻⁵) = 5,033 Hz.
Real circuits have resistance, which damps the resonance and shifts the peak slightly, and parts have tolerance. Treat the result as a starting design value and tune on the bench.
Frequently asked questions
What is the resonant frequency of an LC circuit?
f = 1 ÷ (2π√(LC)). For 1 mH and 1 µF it is about 5,033 Hz.
How do I find the capacitor for a target frequency?
C = 1 ÷ ((2πf)² L). Enter L and the frequency, and leave the capacitance blank.
What happens at resonance?
The inductive and capacitive reactances are equal in size, so they cancel in a series circuit and the energy swaps between the two parts.
Does resistance change the resonant frequency?
Slightly. It damps the response and widens the peak, which this ideal formula ignores.
Are the units henries and farads?
Yes. Use prefixes such as 1m for millihenries or 100n for nanofarads.
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Scope and safety
Low-voltage hobby and study use only. Results are ideal-component arithmetic from the formulas shown, not an engineering design or professional advice. Real parts vary with tolerance, temperature and age, so check the datasheet for every part. Never work on mains-powered circuits from a calculator result, and discharge large capacitors safely before handling.