The 5 Main Ebook Formats

Amazon's Kindle There are so many different ebook formats in existence that trying to get your ebook into every possible format isn’t practical. However it is a good idea to make your ebook available in the most popular ebook formats.

But first a little history.

Ebooks have already been around for a while. In the early days of ebooks people tried various ways of packaging ebooks, even including bundling text files into an EXE file. These “ebooks” typically ran on an application that looked like an internet browser and readers could click on buttons to navigate forwards and backwards through the book.

The problem is that downloading EXE files poses a fairly serious security risk to computers and this format quickly lost popularity as people became more aware of the risks of EXE files and computer viruses. It was only a matter of time until better formats were developed.

The four principal formats for ebooks now are:

  • Portable Document Format (PDF)
  • Kindle Format (AZW, KF8)
  • Mobipocket Format (MOBI, PRC)
  • Epub Format (EPUB)
  • iBooks Format (iBook)

Now let’s look briefly at each of these formats. Then I’ll give you a table that shows at a glance how these formats correlate to the most popular ebook reading devices.

Portable Document Format (PDF)

In 1993 Adobe Systems created the Portable Document Format (PDF) as a standard format for document exchange. When a document was converted to PDF each page was basically an image of the original document. Since almost all computing devices have the capability to read PDFs, the PDF format has been widely adopted and remains one of the preferred methods of providing documents on the Internet today.

However, a problem arose with PDFs. With improvements in technology we started carrying around smaller and smaller devices. First it was laptops and then even smaller devices including Palm Pilots, Blackberries, and mobile phones.

The early versions of PDF were designed for computer screens and were not very suitable for viewing on smaller screens. Because each page was like an image the text couldn’t be “re-flowed” to fit on tiny screens. Readers became frustrated by the need to scroll horizontally as well as vertically to read a single page in a document.

Several new formats for ebooks have been developed which don’t have this problem. The most popular of these follow here.

Amazon’s Kindle Formats (AZW, KF8)

The Kindle format used by earlier Kindles is Amazon’s proprietary ebook format and based on the Mobipocket format (see below) with a different serial number scheme. Amazon purchased Mobipocket in 2005. These earlier Kindle books have the extension .azw

In late 2011, Amazon introduced Kindle Format 8. “KF8 is the next generation file format for Kindle books – replacing Mobi 7. As showcased on Kindle Fire, KF8 enables publishers to create great-looking books in categories that require rich formatting and design such as children’s picture books, comics & graphic novels, technical & engineering books and cookbooks.”

All books sold in the Kindle Store are currently delivered in a format which comprises versions for the older mobi format and Kindle Format 8.

The main extension for Kindle books is now .azw3

Mobipocket (MOBI, PRC)

The Mobipocket ebook format uses XHTML and is based on something known as the Open Ebook standard.

Mobipocket books can be read on the Amazon Kindle and on several other devices that support this format. They can also be read on devices running Mobipocket Reader, a free application from Mobipocket.

Mobipocket files have the extensions .mobi and .prc

The Mobi format is still particularly useful whenever you need to convert a document from  some other format into a format that can be read on the Kindle.

Epub Format (EPUB)

The name ePub comes from “electronic publication”. Epub is a free and open standard for formatting ebooks and became an official standard of the International Digital Publishing Forum in September 2007, superseding the Open Ebook standard.

Epub is the format currently used by the majority of ebook stores, with the exception of Amazon Kindle Store, and including Barnes & Noble Nook Books, Apple iBookstore and Sony Reader Store.

Epub files have the extension .epub

Ebooks in the ePub format can be read on most ebook readers including the Barnes & Noble Nook, Kobo Reader, Sony Reader, Apple iOS and Android devices.

Kindle users cannot currently read ebooks in the ePub format on their Kindles. If a reader with an ePub ebook wants to read it on their Kindle they need to use 3rd-party software to convert the ebook from ePub format to mobi format which the Kindle can read.

IBooks Format (IBA)

This is Apple’s proprietary format based upon the ePub format, introduced in January 2012 with iBooks version 2.0.

Those are the major ebook formats. There are some others but they tend to be associated with earlier devices and are not as popular as those above. PDF technology, incidentally, has advanced considerably and now some PDF documents can also be re-flowed to fit on smaller screens.

The following table summarizes the major reading devices, ebook formats and where to buy them.

Ebook Formats

Table of Major Ebook Readers and Formats

About the Author: Gary McLaren

Gary McLaren is the author of 'The Indie Author's Guide to Publishing Ebooks'. He also manages several web sites for professional writers including Publish Your Own Ebooks and Worldwide Freelance.


  1. Good information. Any author totally against E-books will be left behind I think when it comes to making money. I will always love books but the convenience can’t be beat.

    • Google e-books are on the way and it looks like the iRiver reader is going to be their choice. It takes pdf,word (needs a large font size),epub. As an e-book content editor, I’m obviously an e-book fan.

    • So can I try for all 4 formats to get my ebook out there or is best to just stick to 1?

      • Gina, if you are just trying to get started you could start with one format to get a foot in the door. But if you are serious about your career as an author you should try to reach your readers on the devices they are using to read. You should really aim to have your ebook available in Kindle and ePub formats at the very minimum, and probably PDF if you are selling from your own web site.

  2. A wise writer will have a separate code for each format and publish in all the formats. Why leave money on the table? Don’t forget audio books as well. This is quite a niche market that most writers ignore to their own detriment. It is not just blind people who buy them but commuters who want to kill time while driving.
    John Wilder

    • Thank you. Finally someone else is thinking about those of us with vision challenges. It’s been very disappointing to find out that many books cannot be read by our zoomtext . So yes audio is a preferred media for most of us with vision problems. All authors should consider getting their books put onto audio. I’m working on one now . Thanks again for your insight. Richard

    • John, I agree!

  3. I liked your table. And, liked Mr. Wilder’s comment also; it’s giving me ideas about making an audio book out of my current book.

    • Donna Adkins says:

      There are so many formats for books and I, to, wonder how often these change. What equipment is needed to make an audio book?

      • I wonder why software isn’t developed to convert e-Books into multiple formats the same way we can convert audio and video files multiple formats using a single program. That was the conversion falls on the user rather than the producer and would not require sellers to store all of these files on their servers.

        • Tracy, there is conversion software available but due to Digital Rights Management (DRM) security restrictions many ebooks cannot be converted by end users, in order to help reduce piracy.

          Where possible you can use Calibre software to convert between formats.

  4. This is an informative article and a real keeper. What disturbs me is the rapidity with which these formats change, as older ones become obsolete and new ones are introduced. What are the chances of an ebook remaining relevant/useable in whatever form the author initially chose? In the meantime, a (real) book is a book is a book. I’d like to see some stability in this industry……

  5. I too, am curious about audio formats. Do you have an article speaking to this issue?
    I’m too new at this to know if I could publish in all four of the formats you mention as Mr Wilder suggests.
    Gray Roman

    • Hi and thanks for your comment. We don’t yet have any material on audio formats. I’ve made a note to add some.

      Converting your ebook into all 4 formats isn’t too difficult. It may take longer on your first attempt, but after you have done it once it will be much easier for your subsequent ebooks. If you follow Amazon’s instructions for submitting a Kindle Book, you will actually create a Mobi file which they then convert into the Kindle format. to get the ePub format many authors submit their ebook (in Microsoft Word format) via Smashwords. It takes quite a while to go through their style guide, but you can end up with multiple formats including ePub, PDF and Mobi.

      • Thanks Gary -you’ve answered most of the questions I was about to ask.
        Is there a cost, other than time, to convert an ebook to several different formats?
        Are there likely to be even more formats in the future? Or will commonsense prevail?

      • Thanks for the advice on converting to ebook formats. Is there any conversion software that can be downloaded to help?


        • Calibre software can be handy when converting between formats. Also when preparing your manuscript for the Kindle format you should use Mobipocket to create the Mobi file to upload to Kindle Direct Publishing.

  6. It is good to know the varous formats available to me as a writer.
    Yet I do share some of the concerns cj voiced in the post above.

  7. I have been buying ebooks for many years, long before they became really popular in the marketplace. However, I have yet to write one myself and want to do this soon. Your article explains so much I need to know to get on with it. It is encouraging that PDF technology has advanced so much. Keep writing these excellent articles. Thanks!

  8. Frank Lingo says:

    This is a an interesting way to compare the ebook formats and decide which ones will work for my ebook.
    So far, your advice is the best thing I’ve found available to get my ebook out to the market.

  9. Since POD books became popular in the late 1990s, I have been laying out a number of books in WordPerfect (because it has very useful “Reveal Functions” capability that Word does not). I would then convert WordPerfect to word, and then converting to PDF for upload to BookSurge, now CreateSpace. That way, I have been able to get things done at my own pace, including copy editing, layout, etc. With eBooks, I am faced with four formats, two of which are probably the most widely used. Before, I was able to upload the final PDF file that ultimately was printed. With eBooks, I lack the final step. How do I convert PDF or Word files to the AZW for eBook publication? Is there a converter program available?

    • Hello Mike,

      You can use Calibre and you can generate formats like ePub, mobi, pdf, and many others. Calibre is just free. You can also google step by step instructions on how to do it.

    • Hi Mike, if you visit Kindle Direct Publishing they have a very concise guide on the process to get from Word format to a Mobi file which they will then convert into the Kindle format. I think you’ll find it comparable or even a little easier than what you were doing before.

  10. Thanks, I found this article very helpful. I am in the process of looking which format would be best for my book and this has given me some valuable info. I am wondering, is this information strictly North American, or is it true of the UK as well? I look forward to hearing more.

  11. CJ, Darrell: It sure would be nice to have a guarantee on formats but then again it’s not too difficult to add additional versions of your ebook as new formats emerge. Also, given that most of the major ebook stores and readers are now using the ePub format I doubt that this format will disappear any time soon.

  12. Papa Jim says:

    Very informative article, Gary. My wife and I are both looking to e-publish soon, and your site is proving to be a gold mine of information. Thanks!

  13. What about mobile applications? Are there specific formats for it? I am about to start writing a couple of e-books and that is why I subscribed to this site but sometimes all the tech talk leaves me more than confused. What would you suggest a first-timer into this foray do?

  14. Very informative piece, Gary. I had no idea the Nook reads EPUB formats. I had assumed Barnes & Nobel had developed their own proprietary format. Good to know they’re using an open standard.

  15. In common I suspect with many people looking to publish e-books I consider myself a writer first and foremost, and a techie last of all! I have to confess that the talk of so many different formats sometimes gets me running scared. In your opinion is it really fairly possible for beginners to self-publish in all these different formats or need we be looking at getting outside help to do so?
    If you haven’t already you could make ‘E publishing for dummies’ the subject of your next e-book!

    • Hi Ashley, thanks for your comment. I do have an epublishing book in the works which will come out later. Bottom line, I think most writers can handle the conversion for Kindle format fairly easily. For ePub it depends. I do it through Smashwords, but their guide takes quite a while to work through the first time you do it.

  16. Your coverage of each topic is as usual very informative but I also find the comments by some of your readers even more so. From a marketing standpoint John and Gary are correct in suggesting an ebook be available in all formats to ensure better sales numbers. Richard

  17. Sarah Cox says:

    Finally details on the different Ebook formats that I can understand! This has been very helpful to understand them. Thank you for not overcomplicating the descriptions on each format!

  18. Chris Murano says:

    For those authors who still don’t believe that e-books are the way to go, I would like to refer them to Borders. They felt that print was the only way to go and they are now gone.

  19. Sanjiv Purba says:

    what’s the best format to publish Comic Books?

    • Sanjiv, a good question. I’m not sure the answer – maybe someone else can comment on this?

      • Hi Gary, Hi Sanjiv,

        There are several apps out for the various readers now that are specifically designed for comic books / graphic novels. They require the .cbz or .cbr format. You can do them in epub with limited luck. Ipad is especially tricky. If you need help, just let me know.

  20. Thanks for your response, Gary. It seems this subject generated a lot of interest and comments, as we’re all eager to know more. Thanks for keeping us informed.

  21. I just wanted to add my thanks for clarifying this topic. This is ery useful information in a very concise format. I’ve been a software analyst for many years, but when I went to write my first ebook, I had the exact same question as everyone here – what is/are the best format(s)? Thanks again for taking the time to share. Brian

  22. I’ve found all the information here highly encouraging. I’ve written a small book and have been sitting on it since 2005 knowing that I could never afford to publish it. You’ve now got me very interest in publishing an ebook. I think I can handle the conversion to the correct format.
    How do I get it to the market? Do I create an e-commerce website to sell it?

  23. I am interested in creating an ecookbook are these formats what I would use to create an ecookbook? It would be a book with step by step photographs. Can I do that as an ebook? Thanks.

  24. Jane VanOsdol says:

    Thanks for such useful information. I’m working on a revised edition of my e-book and will be formatting for the top readers.