RC / RL / LC Filter Calculator

Cutoff or resonant frequency, drawn as a Bode plot. Hover the plot to read gain and phase at any frequency.

Filter

R (Ω)

C (F)

L (H)

Bode plot

Green: gain in dB. Orange: phase shift. Red dashes: the cutoff and the −3 dB line.

About this tool

First-order filters

RC: f_c = 1 ÷ (2π·R·C). RL: f_c = R ÷ (2π·L). At the cutoff the output is 3 dB down (about 71% of the input voltage) and shifted 45°. Beyond it the response falls 20 dB per decade.

Series RLC band-pass

f₀ = 1 ÷ (2π√(LC)). At resonance the inductor and capacitor reactances cancel, so the full signal reaches the resistor. Q = √(L/C) ÷ R sets how narrow the pass band is: bandwidth = f₀ ÷ Q.

Assumptions

The plot assumes an ideal source and no load on the output. A load in parallel with the output changes the cutoff; buffer the filter with an op-amp if that matters.