LC Filter Cutoff Calculator
Calculate the ideal LC cutoff or resonant frequency from inductance and capacitance, with tolerance-aware frequency ranges.
Inputs and tolerances
Calculate the ideal LC cutoff or resonant frequency from inductance and capacitance.
The ideal LC frequency is a useful starting point for conducted-noise, supply-input, and interface-filter estimates, but real attenuation depends on source impedance, load impedance, damping, capacitor ESR, inductor resistance, and parasitics.
Nominal results and guaranteed range
- Resonance note: An undamped LC filter can create peaking or ringing near resonance. Practical filters often need damping, ESR, or a lossy element to avoid turning a filter into a noise amplifier.
- This calculator does not model insertion loss, impedance versus frequency, component ESR or ESL, DC bias, saturation, damping networks, or real source and load impedance.
Estimate the ideal LC filter frequency before checking damping and impedance interaction
An LC filter can help with conducted emissions, supply-input filtering, and interface noise suppression. The ideal cutoff or resonant frequency is a useful starting point, but it does not fully predict real attenuation or stability.
Conducted-noise filtering
Use the LC frequency to place a first-pass filter below unwanted ripple or switching-noise regions.
Supply-input filters
Check how an input inductor and capacitor may interact with the source, load, and converter control loop.
Resonance risk
Undamped LC filters can ring, peak, or amplify noise near resonance unless damping is included.
Worked example
A 10 uH inductor and 1 uF capacitor have an ideal LC frequency of about 50.3 kHz. That is a planning value; real insertion loss depends on impedance, damping, and parasitics.
Calculation
fc = 1 / (2*pi*sqrt(L*C)).
fc = 1 / (2*pi*sqrt(10 uH x 1 uF)).
fc ≈ 50.3 kHz.
Design meaning
The LC pair has a natural frequency around 50.3 kHz, but attenuation is not guaranteed by this number alone.
Check source impedance, load impedance, capacitor ESR, inductor DCR, damping, and layout parasitics.
Common mistakes and limits
Treating cutoff as insertion loss
The ideal frequency does not directly say how much attenuation you will get in the real circuit.
Ignoring damping
A very high-Q LC network can ring or peak. Damping may be required for a stable, useful filter.
Forgetting component parasitics
ESR, ESL, DCR, saturation, DC bias, tolerance, and mounting inductance can shift practical behaviour.
Related calculators and next checks
RC low-pass filter calculator
Compare with a first-order RC cutoff when a resistor-capacitor filter is acceptable.
LR time constant calculator
Check inductive first-order settling when resistance dominates the response.
Target impedance calculator
Use for PDN planning when rail droop and transient current define an impedance goal.
Frequency period wavelength converter
Convert filter frequency into period and timing context.
Engineering reference
Equations, assumptions, and design guidance
Calculates the ideal LC cutoff or resonant frequency from inductance and capacitance.
Equations and variables
fc = 1 / (2*pi*sqrt(L*C))T = 1 / fc- L
- Inductance (H)
- C
- Capacitance (F)
- fc
- Ideal cutoff or resonant frequency (Hz)
Assumptions and limitations
Assumptions
- The inductor and capacitor are ideal components.
- The result is the undamped LC natural frequency used as a first-pass filter planning value.
Limitations
- Source impedance, load impedance, damping, ESR, ESL, inductor DCR, saturation, capacitor DC bias, mounting parasitics, and insertion loss are not modelled.
Worked example and design use
10 uH and 1 uF filter
Inputs: L = 10 uH, C = 1 uF
Outputs: fc ≈ 50.3 kHz, period ≈ 19.9 us
Design guidance
- Use the result as a starting point for supply-input filters, conducted-noise filters, and interface noise suppression.
- Check damping and impedance interaction before using an LC filter in a real power path.