T Filter Calculator (with Examples)

A T-filter is used when the input impedance is low. It is an alternative to the very popular Pi filter.

This calculator below requires

  • Cutoff Frequency (Fc)
  • Load Impedance (RL)



Example T Filter Calculation

For a source impedance of 50 Ω and a load Impedance of 1 kΩ, design a low pass filter with a cutoff frequency of 100 kHz.

Use the calculator above, the component values are as follows:

  • L1 = 2.39 mH
  • C2 = 2.12 nF
  • L3 = 796 uH

We can also confirm that for the example in [1] where the source impedance is 50 Ω, load Impedance of 10 kΩ, cutoff frequency of 100 kHz, the calculator provides the following component values

  • L1 = 23.9 mH
  • C2 = 212 pF
  • L3 = 7.96 mH

Advantages of a T-Filter

Used when either the input impedance is low or both input and output impedances are low

Disadvantages of a T-filter

Uses two inductors instead of one as in the case of the Pi Filter. Inductors are more expensive than capacitors and therefore the Pi filter is preferred. Note that a Pi filter can be used when

  • the input impedance is high
  • both input and output impedances are high
  • input and output impedances are equal


[1]  The Art of Electronics by Horowitz and Hill

[2] EMC Filter comparison – T and Pi Filters

Related Calculators

  • Pi Filter – includes four different calculators for both low pass and hi pass filters
  • Power supply pi filters – for both equal and unequal impedance
  • Filter Bandwidth – compute the bandwidth and center frequency from the start and stop frequencies. Useful when you look at the data sheets for SAW filters that don’t provide this info up front.
  • Pi Filter Cutoff Frequency – Use the component values from a schematic to find the cutoff frequencies for both low and high pass filters
  • CLC Filter – provides component values for a desired low pass frequency response
  • Inductor Impedance – calculate the reactance and impedance from the inductance