LC Filter Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Electrical shortcut formulas are useful only when phase, units, and circuit assumptions are kept straight. LC Filter Calculator targets LC cutoff/resonant frequency and shows the relationship behind the number rather than treating it as a black-box design approval. For LC Filter Calculator, a practical cross-check is to change one physically meaningful driver while holding the others fixed and confirm that LC cutoff/resonant frequency moves in the direction predicted by the formula. That simple sensitivity check is often more useful than trusting extra decimal places when a unit or field selection is uncertain.

What this calculator does

The LC Filter Calculator centers on LC cutoff/resonant frequency using the fields that are actually present here: Inductance (L), Capacitance (C), Cutoff frequency (Fc). Rather than treating every box as an independent input, use the equation below to identify the driving quantities and read the remaining fields as derived or supporting values when appropriate.

How to use it

Enter any two among inductance, capacitance, and cutoff frequency. The page uses the pair to solve the third.

How the calculation works

The page uses fc = 1/(2π√LC). It can rearrange to C = 1/[(2πfc)²L] or L = 1/[(2πfc)²C] when a cutoff and the other reactive component are supplied.

Example

With L = 1 mH and C = 1 µF, fc = 1/[2π√(0.001×10⁻⁶)] ≈ 5.03 kHz.

How to interpret the result

For LC Filter Calculator, read LC cutoff/resonant frequency in the context of the equation above. Interpret the result as the output of the stated circuit relationship, not as automatic confirmation that a component, conductor, or installation is adequately rated. Cross-check units and phase convention, then apply real equipment limits and applicable electrical standards separately.

Limitations and notes

This is the ideal lossless LC frequency. Real inductors have winding resistance, core loss, parasitic capacitance, and saturation; capacitors have ESR, tolerance, and self-resonance. A complete filter’s cutoff and Q also depend on source/load impedance and topology.