The Most Common eBook Formats

When self-publishing, how unfair is it that once your book is finished, it’s far from finished? 

Among the myriad post-writing tasks that fall to self-published writers is picking an ebook format. Each of the big self-publishing platforms requires different file formats for the books we put on their sites. Not only that, but formatting code for each is different. What looks great on Kindle might be sketchy on a Nook or a mobile phone. 

So that begs the question: EPUB, MOBI, PDF, or some other thing entirely? 

Where to Start?

There’s a lot of information below, some of it complex and a lot of it nerdy. Honestly, it’s for people who want to get an A or A+ in their publishing journey. For people just starting out, or who are happy with having B-quality work done today instead of A-quality work in a little while, remember this golden rule:

Start with the EPUB format.

Not only should you start with it, but in many cases you can get away with just creating the EPUB file. Thing is, the overwhelming majority of online booksellers support or prefer EPUB. That means you’ve created the file type you’ll use most. 

The only major holdout is Amazon. Even though they are definitely the biggest distributor in the industry, the Coca-Cola, Nike, and Visa of their world, their publishing platform automatically converts from EPUB to the MOBI/AZW3 file that works with Kindle. 

So like I said. About 89% of what you want to accomplish, you can do with an EPUB file. Everything else is just that little extra.

But you should keep reading. The rest is pretty interesting, and you’ll want that A+ eventually.

The Two and Two Halves Publishing Formats

What do I mean by two and two halves instead of three? There are four formats, but two of them are so niche they really only count as half a format each when considering which file format to use. These two and two halves formats are:

  • EPUB
  • PDF
  • MOBI (½)
  • HTML (½)


Epub is a universally agreed upon file format for ebooks, and works reasonably well with most readers. They are resizable and reflowable (meaning they can adjust to the dimensions of different screens and accommodate reader settings), which is why the format is so popular across multiple ebook publishers. They also work with various copy-right protection functions (DRM – digital rights management) intended to reduce or prevent pirating. EPUB files are usually smaller than PDFs, making them easier and cheaper for distributors to manage. 


You probably are already familiar with this file format from your day job, but did you know it stands for Portable Document Format? This file format converts your text document, images, formatted ebook, or whatever into an image as it would print on paper. It standardizes what the file will look like to allow for multiple platforms to use it. That standardization is also its weakness, as it doesn’t adjust to different screen aspect ratios well. The files also tend to be larger than with EPUB.


You hear about MOBI a lot, but it’s literally no longer a thing. Back when almost every platform was using its own file format, Amazon bought a company that used MOBI, and ended up using it for Kindle for long enough that the name stuck in the collective consciousness of epublishing. It’s no longer a thing, but you’ll see AZW, AXW3 and KFX where MOBI used to stand. These descendants are still what Amazon uses, but like I said earlier they can automatically convert EPUB and even DOC files, so we don’t have to worry too much about MOBI. That’s why it counts as a half-format for our purposes. 

In fact, the only MOBI files that Amazon still accepts are for fixed-layout books such as children's books.


HypterText Markup Language is the skeleton on which the internet’s body grew. It’s a simple (even primitive by today’s standards) formatting language that some distributors still use. The reason it sees use in publishing is that every reader and device can use it. You will almost never publish your own work using HTML, but a few niche distributors might ask for your file in HTML so they can convert to their own proprietary format. This is very rare, which is why this one also counts as just a half-format for our purposes. 

Conversions and Creations

Okay. You know what format you want your book in (or you’ve decided to have versions in all four formats just to be ready for anything). You’ve written it in one of the standard formats, and now you need to convert it. Few of the major word processors have this as a default option, but there are plenty of tools that can do it. 

The best free tools include Draft2Digital and Reedsy, which work online, harvest your contact information, and give you a fully formatted document in less than a minute. Amazon offers Kindle Create, though we aren't a fan of the books that it produces. Apex Authors members also have access to the Push Button Book Formatting tool.

You can also use some paid tools to convert you book or to create your book from the start. Our favorite tool is Vellum, which is for Macs only, but Atticus will work across all platforms. 

This market has changed dramatically in the last five years or so. Even then, it could be tricky to find a cost-effective option that turned out a quality manuscript in the format you need. These days, though, it’s pretty easy. 


To recap, or for folks who just want to skim the headlines, here’s the most important parts of what we covered in this article:

  • Different ebook distributors ask for different files when you send them a manuscript. These files are almost never in the format you composed your book in. 
  • EPUB is the most universally used file. You can do almost all of what you need with this format alone. Others are for conquering obscure corners of publishing. 
  • You can use free software to convert your finished book into EPUB format. If you use KDP, it will convert it for you automatically. 

That’s all the basics. Now, it’s time to move forward with your publishing journey and get that manuscript ready to convert!