There is a mistake on DigiKey's Conversion calculator

This page has a mistake for the LC filter configuration:


Remove forward slash (/) at the beginning in the above link.

The equation given for the -3 dB cutoff frequency (for the LC filter) is incorrect. The equation given on the page is the resonant frequency, not the -3 dB cutoff frequency. I made a plot that shows this:


When someone selects LC filter, I recommend two changes:

  1. In “LC Filter Formulas”, change f꜀ to fᵣ.

  2. Change “-3dB Cutoff Frequency” to “Resonant Frequency”

If you would like more information on this, including a derivation of the -3 dB cutoff frequency, please send me an email at michael79749 at

Thank you,

Michael Craft

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Whether one would call that an oversight or an absence of such is unclear, but your point is valid either way. I’ll send a note and see about getting some changes made.

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