LC Resonant Frequency Calculator
Enter inductance and capacitance to calculate the resonant frequency of an ideal LC circuit.
What is resonant frequency?
Resonant frequency is the natural frequency at which a system prefers to oscillate. In electronics, resonance is especially important in circuits that contain an inductor (L) and capacitor (C). At one specific frequency, the inductor’s reactance and the capacitor’s reactance cancel each other out, creating resonance.
That frequency matters because it determines where a circuit can tune, filter, or transfer energy most effectively.
Resonant frequency formula (LC circuit)
For an ideal LC circuit, resonant frequency is:
f = 1 / (2π√(LC))
- f = resonant frequency in hertz (Hz)
- L = inductance in henries (H)
- C = capacitance in farads (F)
- π ≈ 3.14159
If you use mH, µH, nF, or pF in real-world values, convert them to base SI units first. This calculator handles those conversions automatically.
Quick interpretation rule
- Larger L or C gives a lower resonant frequency.
- Smaller L and C gives a higher resonant frequency.
How to use this resonant frequency calculator
- Enter your inductance value and select the correct unit.
- Enter your capacitance value and select the correct unit.
- Click Calculate.
- Read the results in Hz and scaled engineering format (kHz, MHz, etc.).
The result panel also shows angular frequency and oscillation period, which are useful in design and analysis workflows.
Worked example
Suppose your circuit has:
- L = 10 mH
- C = 100 nF
Converted to base units:
- L = 0.01 H
- C = 0.0000001 F
Apply the formula:
f = 1 / (2π√(0.01 × 0.0000001)) ≈ 5032.92 Hz
So the resonant frequency is approximately 5.03 kHz.
Where resonance is used
1) RF tuning and radio receivers
Tuned circuits choose one signal frequency from many. Resonance is the foundation of channel selection in many communication systems.
2) Filters and signal processing
Band-pass and notch filters rely on resonance behavior to pass desired frequencies and suppress unwanted ones.
3) Power electronics and wireless power
Resonant converters and wireless charging systems use carefully selected resonant frequencies to improve efficiency.
4) Sensors and measurement systems
Many sensing techniques track frequency shifts caused by changes in capacitance, inductance, mass, or geometry.
Practical considerations
The ideal formula is a starting point. Real circuits may behave slightly differently due to non-ideal effects:
- Component tolerances (e.g., ±5% capacitors)
- Parasitic resistance in coils and capacitor ESR
- Temperature drift
- PCB trace inductance/capacitance
- Loading from connected stages or measurement tools
For precision applications, include these non-ideal effects in simulation and measurement validation.
FAQ
Is resonant frequency the same as natural frequency?
In many contexts, yes. “Natural frequency” is broad; “resonant frequency” usually refers to the frequency where response peaks due to energy exchange between storage elements.
Can this calculator be used for series and parallel RLC circuits?
This page calculates the ideal LC resonance point. Real series and parallel RLC circuits include resistance, which affects peak response and bandwidth, though resonance often remains close to the LC formula.
Why are there multiple output formats?
Engineering work spans wide frequency ranges. Seeing values in Hz, kHz, MHz, or GHz makes interpretation faster and helps avoid scaling mistakes.
Final note
This resonant frequency calculator is a quick design aid for students, hobbyists, and engineers. Use it to estimate resonance, then verify your final design with component tolerances, simulation, and bench testing.