⚡ 2nd Order LC Low Pass Filter Calculator
Resonant frequency · Inductive reactance · Q factor · Find L or C
Calculate Resonant Frequency fr
Results
fr — Resonant Frequency
XL — Inductive Reactance at fr
R — Load Resistance (from Q)
Find L from fr & C
Result — L
L = 1 / (4π² · fr² · C)
Find C from fr & L
Result — C
C = 1 / (4π² · fr² · L)
Key Formulae
Resonant frequency:
fr = 1 / (2π · √(L·C))
Inductive reactance at fr:
XL = 2π · fr · L
Quality factor (load resistance):
Q = R / XL → R = Q · XL
Find inductance:
L = 1 / (4π² · fr² · C)
Find capacitance:
C = 1 / (4π² · fr² · L)
About This Calculator
This calculator is for the second order LC low pass filter — compute resonant frequency, inductive reactance and load resistance from L, C and Q, or find L or C from a known resonant frequency.
Q Factor & Frequency Response
The Q of the filter is given by Q = R / XL, where XL is calculated at the resonant frequency. High Q produces a peak in the frequency response. For a maximally flat Butterworth response, use Q = 0.707.
High Q — peaking response
Q = 0.707 — maximally flat (Butterworth)
Quality Factor Definition
Q = (Energy stored in reactive component) / (Energy dissipated)
or equivalently: Q = XC / Rw = XL / Rw
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