Resonant Frequency Calculator
Find the resonant frequency of an LC circuit.
Results update as you type.
How it works
The resonant frequency is the frequency at which an inductor-capacitor, or LC, circuit naturally oscillates, and this calculator finds it from the inductance and capacitance. You enter the inductance in henries and the capacitance in farads, and it returns the resonant frequency in hertz. At resonance, the energy sloshes back and forth between the magnetic field of the inductor and the electric field of the capacitor, and the inductive and capacitive reactances become equal and opposite, canceling out. This makes the circuit respond most strongly at that frequency, which is the basis for tuning radios, building oscillators and filters, and countless applications in electronics and communications. The formula shows that resonant frequency depends inversely on the square root of the product of inductance and capacitance, so increasing either component lowers the frequency, and decreasing them raises it. This inverse-square-root relationship means you must change the components by a factor of four to halve or double the frequency. Engineers and hobbyists use this to design tuned circuits, select components for a target frequency, and understand oscillator behavior. Because the values in real circuits span a huge range, capacitance is often in microfarads or picofarads and inductance in millihenries or microhenries. Enter the inductance and capacitance to compute the resonant frequency.
f = 1 / (2π√(LC))
The resonant frequency of an LC circuit equals one divided by two pi times the square root of the inductance times the capacitance. At this frequency the inductive and capacitive reactances cancel, and the circuit oscillates most readily. Larger inductance or capacitance lowers the resonant frequency, while smaller values raise it.
Source:Electrical engineering
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter inductance and capacitance.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Resonant frequency updates instantly as you type — no button to press.
Frequently asked questions
What is resonant frequency?
Resonant frequency is the frequency at which an LC circuit naturally oscillates with the greatest amplitude. At this frequency the inductive and capacitive reactances cancel, so the circuit offers the least opposition to oscillation. It is fundamental to tuning, filtering, and oscillator circuits throughout electronics and radio.
How do you calculate resonant frequency?
Use the formula one divided by two pi times the square root of inductance times capacitance. Enter the inductance in henries and capacitance in farads, and the calculator returns the frequency in hertz. Because real components are small, remember to convert microfarads and millihenries to base units before entering them.
How do inductance and capacitance affect the frequency?
Resonant frequency is inversely proportional to the square root of the product of inductance and capacitance. Increasing either lowers the frequency; decreasing either raises it. Because of the square root, you must change a component fourfold to halve or double the frequency, which matters when designing tunable circuits.
What is resonant frequency used for?
It underlies radio tuning, where a variable capacitor selects a station's frequency, as well as oscillators that generate signals, band-pass and band-stop filters, wireless charging, and metal detectors. Any circuit that must respond to or generate a specific frequency relies on setting its resonant frequency through chosen inductance and capacitance.
What happens at resonance?
At resonance, the inductor's and capacitor's reactances are equal and opposite and cancel, so a series LC circuit shows minimum impedance and a parallel LC circuit shows maximum impedance. Energy oscillates between the two components with little loss, producing a strong response at that single frequency, which is what makes tuning possible.