KFX to epub conversion via Calibre?

angel44e · 10-14-2025, 04:20 AM

Hello! I just don't know where to ask that question ( so many topics there are ) or is there any similar problem.

I usually convert from KFX files ( my kindle amazon boooks ) to epub and pdf files . And I don't change anything in settings ( just leave them as default ) and they are converted normally and fully readable files till now.

But one book that I've converted in that way taken too much time to convert ( from 10MB KFX file ) and output files are too large - 89 MB epub and 113 MB pdf. PDF file text is small and I should quite zoom pages so to be readable and epub file text is too small and not readable at all.

Is it depends on metadata of book or should be change some settings of input/output file?

How could I solve that problem? Any help appreciated

JSWolf · 10-14-2025, 10:10 AM

Open the ePub in the calibre editor and have a look at the code. You should be able to fix the font size problem.

angel44e · 10-14-2025, 11:57 AM

Quote:

Originally Posted by JSWolf

Open the ePub in the calibre editor and have a look at the code. You should be able to fix the font size problem.

Thanks! I've seen so many options to check and to change!

And there are 2 or 3 for fonts.I've asked ChatGPT,but it didn't help me at all.

I've done all settings as AI adviced,but result is same as my previous converted epub.

And I don't know what and where to change in editor

Jaws · Today, 02:17 AM

One additional step: Make sure you understand at least a little CSS. What's describer here is very probably in the style definitions, not in the individual files (often one or more for each chapter and element like the title page) — and ChatGPT gets darned near everything about working with CSS either incomplete or flat wrong (it's probably parsing things the way a certain subset of programmers would, or mixing versions).

A basic learning resource is:
https://learn-css.org/

A basic reference that actually works with most epub readers, without encouraging poorly-supported but really cool stuff, is:
https://www.w3schools.com/cssref/

Here's an example, from the top of a file of a book converted from KFX:

Code:

 <body class="class1">
<p class="class_12">xxxxxtitlexxxxx</p>
<p class="class_13">xxxxxauthorxxxxx</p>
<p class="class_14">beginmaintext

You would need to check the font size in the stylesheet (a segment in the editor right below the actual content) for all four of the classes, because the too-small font size could be in class1 (for the body) and inherited by everything else.

This is a really, really common problem with books originally printed from the mid-1980s through about 2004, then hastily converted by the publisher (with no real proofreading) and put up on Amazon. In other words, it's not your fault; it's not Calibre's fault or the plugin's fault; it's only partly Amazon's fault. (You really don't want to have sat in production meetings with graphic designers arguing about the best workarounds in PageMaker 5 or any version of Quark to get exact spacing in tables correct when the first-edition printing company used M-T machines and the new one uses Linotype machines... and that's assuming that the authors hadn't "helpfully" sent the revised tables over as LaTeX files...)

10-14-2025, 04:20 AM	#1
angel44e Member Posts: 11 Karma: 110 Join Date: Feb 2025 Device: kindle android	KFX to epub conversion via Calibre? Hello! I just don't know where to ask that question ( so many topics there are ) or is there any similar problem. I usually convert from KFX files ( my kindle amazon boooks ) to epub and pdf files . And I don't change anything in settings ( just leave them as default ) and they are converted normally and fully readable files till now. But one book that I've converted in that way taken too much time to convert ( from 10MB KFX file ) and output files are too large - 89 MB epub and 113 MB pdf. PDF file text is small and I should quite zoom pages so to be readable and epub file text is too small and not readable at all. Is it depends on metadata of book or should be change some settings of input/output file? How could I solve that problem? Any help appreciated Last edited by angel44e; 10-14-2025 at 08:24 AM.

Today, 02:17 AM	#4
Jaws JCL Punch-Card Collector Posts: 87 Karma: 34468 Join Date: Jun 2014 Location: Antarctica Device: Aggressively Device Independent	One additional step: Make sure you understand at least a little CSS. What's describer here is very probably in the style definitions, not in the individual files (often one or more for each chapter and element like the title page) — and ChatGPT gets darned near everything about working with CSS either incomplete or flat wrong (it's probably parsing things the way a certain subset of programmers would, or mixing versions). A basic learning resource is: https://learn-css.org/ A basic reference that actually works with most epub readers, without encouraging poorly-supported but really cool stuff, is: https://www.w3schools.com/cssref/ Here's an example, from the top of a file of a book converted from KFX: Code: <body class="class1"> <p class="class_12">xxxxxtitlexxxxx</p> <p class="class_13">xxxxxauthorxxxxx</p> <p class="class_14">beginmaintext You would need to check the font size in the stylesheet (a segment in the editor right below the actual content) for all four of the classes, because the too-small font size could be in class1 (for the body) and inherited by everything else. This is a really, really common problem with books originally printed from the mid-1980s through about 2004, then hastily converted by the publisher (with no real proofreading) and put up on Amazon. In other words, it's not your fault; it's not Calibre's fault or the plugin's fault; it's only partly Amazon's fault. (You really don't want to have sat in production meetings with graphic designers arguing about the best workarounds in PageMaker 5 or any version of Quark to get exact spacing in tables correct when the first-edition printing company used M-T machines and the new one uses Linotype machines... and that's assuming that the authors hadn't "helpfully" sent the revised tables over as LaTeX files...)

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10-14-2025, 10:10 AM	#2
JSWolf Resident Curmudgeon Posts: 80,559 Karma: 150249619 Join Date: Nov 2006 Location: Roslindale, Massachusetts Device: Kobo Libra 2, Kobo Aura H2O, PRS-650, PRS-T1, nook STR, PW3	Open the ePub in the calibre editor and have a look at the code. You should be able to fix the font size problem.

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