How to use this calculator

Choose the filter, enter the component values and the frequency of interest. The plot spans two and a half decades either side of the corner or resonant frequency.

Formulas

RCf_c = 1/(2πRC)

RLf_c = R/(2πL)

Series RLCf₀ = 1/(2π√(LC)), Q = (1/R)√(L/C), BW = R/(2πL)

GaindB = 20 log₁₀|H|

Worked example

RC low-pass, R = 1 kΩ, C = 0.1 µF (the default)

f_c = 1/(2π × 1000 × 10⁻⁷) = 1591.5 Hz.
At 1 kHz, |H| = 1/√(1 + (1000/1591.5)²) = 0.847, or −1.45 dB, with phase −32.1°.

Frequently asked questions

What does −3 dB mean?

Half power: the output amplitude is 1/√2 of the input. It defines the cutoff frequency of first-order filters.