LC Resonant Frequency Calculator
Use this tool to calculate the natural resonance of an LC tank circuit using f = 1 / (2π√(LC)).
What is LC resonant frequency?
In electronics, an LC circuit (also called a tank circuit) combines an inductor (L) and capacitor (C). The resonant frequency is the point where energy oscillates back and forth between the magnetic field of the inductor and the electric field of the capacitor. At this frequency, the circuit can strongly pass or reject signals depending on whether it is arranged in series or parallel.
LC resonance is foundational in radio tuning, oscillators, impedance matching, RF filters, and communication systems. Whether you are building a hobby transmitter, tuning an antenna network, or studying circuit theory, knowing the resonant frequency quickly is essential.
Core formula
f0 = 1 / (2π√(LC))
where L is in henries (H), C is in farads (F), and f0 is in hertz (Hz).
If you enter values in µH, nH, nF, or pF, the calculator converts them automatically to SI units before computing the final frequency.
Quick unit reference
- 1 mH = 10-3 H
- 1 µH = 10-6 H
- 1 nH = 10-9 H
- 1 µF = 10-6 F
- 1 nF = 10-9 F
- 1 pF = 10-12 F
How to use this LC calculator
- Enter the inductor value and choose the proper unit.
- Enter the capacitor value and choose the proper unit.
- Click Calculate Resonance.
- Read the result in Hz plus supporting outputs (kHz/MHz, angular frequency, and period).
Example calculations
Example 1: AM tuning section
Suppose L = 250 µH and C = 365 pF. The resonant frequency is around 527 kHz, which is in the AM broadcast range. This is why variable capacitors are common in older radio tuning circuits.
Example 2: RF front-end
With L = 10 µH and C = 100 pF, resonance is roughly 5.03 MHz. Small component changes can move frequency significantly, so tight tolerance parts are important in RF design.
Practical engineering notes
Real components are not ideal
Real inductors include winding resistance and parasitic capacitance. Real capacitors include ESR and inductive lead effects. These parasitics shift resonance and reduce Q factor.
Loaded vs unloaded resonance
In a real circuit, surrounding stages and source/load impedance alter the effective resonant point. The measured resonance on a bench may differ from textbook calculations, especially at higher frequencies.
Tolerance matters
- Inductor tolerance (e.g., ±5%) shifts frequency.
- Capacitor tolerance and temperature coefficient can drift tuning.
- At RF, PCB layout and trace inductance become part of the circuit.
Common mistakes to avoid
- Mixing units (for example, typing µH while selecting mH).
- Using zero or negative values for L or C.
- Ignoring parasitics in high-frequency or precision designs.
- Assuming resonance behavior is identical for series and parallel LC networks.
Need to solve for L or C instead?
If frequency and one component are known, rearrange the resonance formula:
- L = 1 / ((2πf)2 C)
- C = 1 / ((2πf)2 L)
This is useful for filter design, oscillator prototyping, and selecting replacement parts for tuned circuits.
Final thoughts
This LC resonant frequency calculator is designed for fast, reliable estimates during design and troubleshooting. For final hardware validation, always confirm with measurement tools such as an LCR meter, network analyzer, or oscilloscope-based sweep method.