Over the years, there have been many file types used to create books, from eBooks to Print Books.
Those file types evolve, some are discontinued, but one in particular currently reigns supreme. (Hint: it rhymes with GLEEHUB).
- The most common file types for eBooks and print
- Other file types common for ebooks
- Which file types you should use
Table of contents
There are three primary book file types that you should be familiar with, though one of them is already on its way out.
Why You Should Trust Me
So I've been writing and formatting books for a long time. 10+ years as of this writing.
But I actually found formatting to be a huge pain, which is why I actually created my own formatting software that solved all my problems. I called it Atticus.
But this isn't meant to be a sales pitch. I just want to make sure it's clear that I know what I'm talking about. The amount of research that went into not only formatting my own books, but also creating a formatting software is huge.
I researched everything, from tiny margin requirements, to the specific type of quotes to use (curly or straight, it makes a difference).
And yes, of course, that includes book file formats.
So if all that makes sense, hopefully you'll come along with me as show you everything I've learned.
EPUB (.epub)
An EPUB file is the most widely used, and best supported format for an eBook. It plays on virtually all devices, including:
- Kindle
- Nook
- Computers
- Tablets
- Smartphones
- Most ebook readers
Most EPUB files are reflowable, which means that the text and images will shift to fit the screen size of the device.
However, this doesn’t have to be the case. EPUBs are versatile enough that they can be programmed to have fixed layouts if needed.
A fixed layout usually has designs that are dependent on the layout of the text and images. These layouts are common in children’s books, image/infographic-heavy non-fiction books, and comic books.
Thankfully, you can have both reflowable and fixed layout books with EPUB.
EPUB book files are based on coding standards such as XHTML, XML, CSS, and compatible with HTML5, MathML, JavaScript, and vector graphics like the popular SVG file type.
In other words, it’s a powerful file.
Formerly, EPUBs were not published on Amazon, requiring the MOBI instead. But that has since changed. EPUBs can now be used on Amazon, and are now the recommended ebook type there.
When Should You Use an EPUB file?
Since almost all eBook vendors use EPUB files these days, you should default to the EPUB in almost every instance where you would need an eBook. Thankfully, programs like Atticus will automatically generate an EPUB file for you when you're ready to format and publish your book.
Print, however, uses a different file format…
PDF (.pdf)
PDFs are another common type of book file. However, they are better served in constructing your print books, and not as eBooks.
The PDF was a file type created by Adobe, and has gained widespread use ever since. They are useful for any book that requires a fixed layout, especially in print.
When Should You Use a PDF?
You should use a PDF when uploading a print book to Amazon, IngramSpark, or another print service. They should never be used as eBooks. If you need the fixed layout that a PDF can provide, use the fixed EPUB format.
Creating a print-ready PDF can be tricky, which is why programs like Atticus or Kindle Create are essential tools when formatting your book.
Atticus will not only let you create beautiful PDFs with all the formatting guidelines in place for Kindle Direct Publishing or IngramSpark, but is also available on virtually every platform, and is a lifetime purchase option so you get all future updates for free (and believe me, there are many amazing updates coming down the pipeline).
MOBI (.mobi)
Previously, the MOBI file was another important file type to be aware of, as it was the primary file used for uploading a book to Amazon’s KDP Marketplace.
However, all that has changed.
Amazon now accepts, and even recommends, that you upload your book as an EPUB, and they eventually completely did away with the MOBI file.
Essentially, the MOBI is dead.
Amazon now has two other eBook formats, AZW3 and KPF, which are the primary book file formats that Amazon uses on the user end.
When you submit a MOBI, EPUB, DOCX, or any other accepted file type to Amazon, it will usually convert to AZW3 or KPF.
Which is better, MOBI or EPUB? In today's market, EPUB is the better eBook format to use, but there might be some special circumstances where a MOBI file is warranted.
AZW3 (.azw3) and KPF (.kpf)
AZW3 and KPF are worth knowing because they are the primary file types used by Amazon today, using their own digital rights management (DRM) system..
- AZW3, also known as KF8 is the eBook file that Amazon uses on its devices. It can only be viewed on Amazon devices.
- KPF, a variant of the older KFX file, is a file type generated using Amazon’s own book formatting software, Kindle Create.
In addition to the EPUB, KDP also recommends using a KPF file type because it will integrate seamlessly with their devices. That said, doing so is not required, and Amazon will automatically convert your EPUB to the correct format upon upload.
If you want to go the extra mile, you can convert your ebook to a KPF format ahead of time and confirm that everything works the way it should, then submit to Amazon.
However, you don’t need to worry much about AZW3 and KPF, since these are just file types that are used on Amazon's end, and the EPUB is more than sufficient for submitting to Amazon.
Format Beautiful Professional Books
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Check It OutOther Formats
In addition to the five formats mentioned above, here are a handful of other book file types you might encounter, though none of them are particularly significant for most authors.
- Mobipocket: An older e-book format used by Amazon that was officially discontinued in 2016.
- AZW: An older version of AZW3.
- DOC/DOCX: These will work as ebooks when uploaded to KDP, but if you have even a modest amount of formatting, it very often doesn’t translate well.
- RTF/TXT: These file types will also (technically) work with KDP, but have no advanced formatting features.
- IBOOKS: This file type is used by Apple, but you can still use an EPUB when submitting to Apple Books.
- FB2: This is a popular ebook file type in Russia.
- Comic Book Archive: There are a number of file extensions that you’ll find for comic books, such as .cbz, .cbr, .cb7, and more. These are essentially ZIP files that can be unzipped to see a series of images.
For a comprehensive list of book file types, visit this page.
What is DRM?
DRM stands for Digital Rights Management, and is a form of digital protection that vendors like Amazon or Google use to protect their eBooks from widespread piracy. Basically it keeps the digital files from being copied and used on other devices.
While most eBooks have some form of DRM, Amazon does give you the option of removing it from your eBook formatting files
What is the Best File Format for Books?
The best eBook format is EPUB, and the best print file is a PDF. I have a comprehensive comparison of the main file types that you can read, but the bottom line is this:
For Ebooks
Ever since KDP allowed the use of the EPUB, it has become virtually the only ebook file type that is most compatible with all the major ebook retailers, as you can see below.
Not only that, it is also open source, extremely versatile, and widely accepted as the best version. I highly recommend that you use the EPUB as your first choice.
| Marketplace | EPUB | MOBI/AZW3 | HTML | |
|---|---|---|---|---|
| Amazon |  | | (no embedded formatting) | (only on the Kindle app, not the Fire tablet) |
Apple Books | | | ||
| Kobo | | | | |
| Barnes & Noble Press | | |||
| Google Play Books | | |
The one possible exception I would make might be a KPF file, created using Kindle Create. Using this file is one of the best ways to ensure that your book integrates seamlessly with Amazon.
That said, the EPUB works perfectly fine for most people, and it’s easy to catch any issues by using the kindle previewer when uploading to KDP.
For Print
If you are uploading to KDP Print or IngramSpark, the best option is using a PDF file. This helps you keep the fixed layout that you need for a seamless digital print experience.
A formatting software is a great way to create these print PDFs. See my recommendations for best formatting software here.
Which File Format Will You Use?
Now that you know the ins and outs of the main book file types, which one will you use? Let us know below what your experience is with these file types.
Additionally, if you want to know more about formatting or converting between files, check out these resources:
- Kindle Direct Publishing 
