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RL Filter Calculator — Cutoff, Reactance & Time Constant

Calculate first-order RL cutoff frequency, inductive reactance, time constant and ideal low-pass/high-pass magnitude at a test frequency.

Results

Cutoff 1,591.549 Hz
Reactance 62.83185 Ω
Gain 0.846733
Gain -1.44507 dB
τ 0.0001 s

Formula and assumptions

fc=R/(2πL); τ=L/R; XL=2πfL.

100 Ω with 10 mH gives fc ≈ 1.592 kHz.

  • Ideal series RL network.
  • Winding resistance and source/load impedance are excluded unless included in R.

Frequently asked questions

What sets RL cutoff?

Resistance and inductance set the corner through fc=R/(2πL).

Does inductor resistance matter?

Yes in real hardware; include relevant series resistance when appropriate.

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