calibre is the ebook converter most people end up with, and for good reason: it reads almost every format an ebook ships in and writes the ones readers actually want. This guide is the whole task in one page. Add the book, pick the output format, set the device profile, convert, check the file.
The steps name the menus in calibre-zen, which is calibre with a calmer window. They are calibre’s own menus, so the same clicks work in plain calibre. The controls here were checked against version 0.4.1, on calibre 9.15.0.
What a calibre ebook converter actually does
Conversion is not a rename. calibre opens the source file with an input plugin, turns it into XHTML, runs that through its transform steps, then writes the result with an output plugin. The calibre manual describes that pipeline in order: input plugin, transform, output plugin.
That explains the one thing people find odd. The output quality depends far more on the input than on the settings. A clean EPUB converts to anything well. A PDF built for print loses its layout, because the pipeline has no page layout to preserve on the way out.
Which formats it writes
The manual lists 30 input formats and 20 output formats, and says every input in its list converts to every output. The outputs are:
- EPUB, the open standard most stores and libraries use.
- AZW3, Amazon’s newer Kindle format.
- MOBI, the older Kindle format.
- KEPUB, for Kobo readers.
- PDF, for printing and for fixed layouts.
- DOCX, for going back to a word processor. ODT is input only, so DOCX is the route out.
- FB2, LIT, LRF, PDB, PMLZ, RB, SNB, TCR, TXT, TXTZ, HTMLZ, OEB, ZIP.
Comic archives are input only, so a CBZ or CBR can become an EPUB but nothing becomes a CBZ.
1. Add the book
Click Add books in the top toolbar and pick the file. It lands in the library and shows up in the book list.
If you already have a calibre library, point the app at it and everything is there: books, covers, tags, custom columns. The full comparison of the two apps is in calibre-zen vs calibre.
2. Pick the output format
Select the book, click Convert books, and choose Convert individually. The conversion dialog opens with the book’s title in the top left corner.
The Output format dropdown sits at the top right. Open it and pick your target. It lists the formats calibre writes, which is the list in the section above, not the ones it reads.
The dropdown keeps your pick for that book only. Default settings for every future conversion live under Preferences → Conversion, so a book you converted once keeps its own settings until you clear them.
3. Set the output profile in Page setup
Open the Page setup section of the same dialog. It holds the Input profile and the Output profile.
The profile is how calibre knows what screen it is writing for. It sets the screen size, and in some formats it resizes images to fit. The manual’s advice is specific:
- Converting to MOBI or AZW3: choose one of the Kindle output profiles.
- Anything else, on a modern reader: choose Generic e-ink HD.
If you know the exact device, pick its profile instead. A phone and an e-ink reader want different page sizes, and that is the setting that decides it.
4. Convert and check the file
Click OK. A box in the bottom right tracks the job. When it finishes, the book row’s format column gains an entry for the new format.
The file sits in the library folder, in the sub-folder calibre made for that author and title. Right-click the book and choose Open containing folder to see it. The original file is still there, untouched, so you end up holding both formats.
To check the result, right-click the book and choose View format, then the new one. calibre’s viewer opens exactly what was produced, which is the fastest way to catch a bad conversion before it reaches a reader.
5. Convert a batch at once
Select several books, click Convert books, and choose Bulk convert. The options are set once for the whole batch.
That is the catch: only group books that need the same output format and the same profile. Per the manual, bulk conversion ignores per-book settings except metadata and input options, so a mixed batch gets one set of choices.
Which format should you pick
- EPUB is the default answer. It reflows, most stores sell it, and the common reader apps on a phone, tablet or computer open it.
- AZW3 is for a Kindle you load by cable. It keeps more formatting than MOBI.
- MOBI only when an older Kindle or an old app refuses anything else. Newer Kindles do not need it.
- PDF when the page layout is the point: a comic, a textbook, a design-heavy file. Do not use it for a novel you want to read on a phone.
- KEPUB for a Kobo, when you want the reader’s own page numbering and chapter progress to work.
If you are still choosing between calibre and something else, calibre alternatives covers what the other converters do and do not handle.
When conversion will not help
Three cases come up again and again, and none of them is fixed by a setting.
The book has DRM. The calibre manual is direct: most purchased EPUB books have DRM, and it prevents calibre from opening them. You can still keep such a book in the library and send it to a reader, but the converter will not touch it.
The input is a PDF. The manual lists what PDF input cannot do: complex, multi-column and image-based documents are not supported, vector images and tables are not extracted, and links and tables of contents are lost. A plain single-column novel is the case it handles; a magazine layout is not.
The output format cannot hold what you want. Fixed layout, colour, embedded fonts and complex tables all depend on the target format. Converting down loses something, and no setting brings it back.
The app is free to download and use. If you want to see what changed in the window before you install, the docs cover the install and what moved.
