Resonant Frequency Calculator
The resonant frequency calculator determines the natural oscillation frequency of an LC (inductor-capacitor) circuit. When an inductor and capacitor are connected together, they exchange energy at a specific frequency where inductive reactance equals capacitive reactance. This frequency, known as the resonant or natural frequency, is fundamental in radio communications, filter design, oscillator circuits, and antenna matching networks. Engineers and hobbyists use resonant frequency calculations to tune circuits to specific channels, design bandpass filters, and ensure maximum power transfer between components. Enter the inductance in microhenries and capacitance in picofarads to instantly calculate the resonant frequency. The tool also accepts values in other unit prefixes using the unit selector. Results are displayed in Hz, kHz, and MHz for convenience.
Resonant frequency formula
f = 1 / (2 * pi * sqrt(L * C))
Where f is resonant frequency in Hz, L is inductance in Henries, C is capacitance in Farads, and pi = 3.14159. The angular frequency omega = 2 * pi * f = 1 / sqrt(L * C).
How LC resonance works
- At resonance, inductive reactance XL = 2 * pi * f * L equals capacitive reactance XC = 1 / (2 * pi * f * C).
- Energy oscillates between the magnetic field of the inductor and the electric field of the capacitor.
- Series LC circuits have minimum impedance at resonance; parallel LC circuits have maximum impedance.
- Real circuits also have resistance, which limits the peak response and determines the Q factor.
- Increasing L or C lowers the resonant frequency; decreasing either raises it.
Resonant frequency: frequently asked questions
What is resonant frequency?
Resonant frequency is the natural frequency at which an LC circuit oscillates with minimum impedance and maximum energy transfer between the inductor and capacitor. At resonance, the inductive and capacitive reactances are equal and cancel each other out.
What is the formula for resonant frequency?
The resonant frequency formula is f = 1 / (2 * pi * sqrt(L * C)), where f is frequency in Hz, L is inductance in Henries, and C is capacitance in Farads. This is derived from setting inductive reactance equal to capacitive reactance.
Why is resonant frequency important in electronics?
Resonant frequency determines how circuits respond to different signal frequencies. Radio tuners use LC circuits at resonance to select a specific station. Filters, oscillators, and antenna matching networks all rely on resonant frequency principles.
What happens below and above resonant frequency?
Below resonance, the circuit behaves capacitively (capacitive reactance dominates). Above resonance, it behaves inductively (inductive reactance dominates). At resonance, the impedance is purely resistive and at its minimum for series circuits.
How do I convert between nH, uH, mH for inductance?
1 Henry (H) = 1,000 millihenries (mH) = 1,000,000 microhenries (uH) = 1,000,000,000 nanohenries (nH). Similarly for capacitance: 1 F = 1,000 mF = 1,000,000 uF = 1,000,000,000 nF = 1,000,000,000,000 pF.
Official sources
- NIST: Electrical Measurements - NIST Physical Measurement Laboratory.
- IEEE: IEEE Educational Resources on Circuit Theory.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.