The title reveals the gist of my question. I simply don't want to have to include [per-mode=symbol] every single time I call \SI{value}{unit} for a unit which includes a fraction. How do I make this the default for a given document?

  • 1
    May I ask which version of siunitx you are using? The \SI{}{} style seems like the older version of the package. The new package uses \qty{value}{unit} to write numbers and units, \unit{unit} to express only units, and \num{} to write only numbers. Jan 30, 2023 at 15:06
  • @Ginko-Mitten Thanks for pointing that out. I have no clue how to check package versions, but I know it comes from texlive-full from the stable Debian Bullseye repos. You know all the jokes about Debian being slow on updating their repos. ;)
    – GPWR
    Jan 30, 2023 at 15:19
  • check your .log file or type tlmgr info siunitx in your terminal to get this info. If you want the latest installation, try using the instructions on: fahim-sikder.github.io/post/installing-texlive-latest-ubuntu. The instruction set is for 2021, but you can change the year to 2023 in each instruction code and get the latest version, if you wish. All the best. :) Jan 30, 2023 at 15:49
  • @Ginko-Mitten Thanks! Super useful! God bless.
    – GPWR
    Jan 30, 2023 at 16:59

1 Answer 1


In the preamble you can do the following:


That should make / as the default per symbol.

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