I'm using calibre to convert my books from pdf to mobi. My issue is that I have hundreds of books that are already in the mobi format and I'm looking only to convert the books that aren't already in the mobi format.

When I try to convert all of my books it converts the pdf books into mobi even if they are already in mobi. To convert my book collection is going to take many hours, and I'm wondering if there is a way to mass convert books that aren't already in the output format.

Thank you. Will accept any work around that accomplishes this.

  • Will calibre give me a list of books not in a specific format?
    – Ravenous
    Commented Jul 17, 2016 at 19:23
  • What operating system are you running calibre on, and how comfortable are you with the command line? :-) I might not understand the question correctly, but if you want to convert some of your books (and not all), you might try (1) finding that subset of books in format FOO and then (2) sending the list of those books in FOO format to the calibre command line. Link to Calibre command line manual.calibre-ebook.com/generated/en/cli-index.html Could you expand your question with a sample of what you want to convert and what you do not want to convert? Thank you. Commented Jul 18, 2016 at 4:00

1 Answer 1


I'm surprised nobody has responded in six months, sorry I haven't been here :-(

I do this all the time.

You want to convert everything that has formats:"=PDF" and doesn't have formats:"=MOBI". You can just put those conditions in the search box, or in the tag browser:

  • Select the PDF format (which will place a big + beside it), then
  • ctrl-select the MOBI format twice, instead of a + there'll be a -

You'll see the following selection string in the search box: not formats:"=MOBI" or formats:"=PDF". Now you have all the books that are either not MOBI or are PDF. That's not nearly what you want, but now just change the or to and (or delete it—no conjunction is the same as using and) in the search box and you have all of the PDFs that don't also have a MOBI.

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