It is a basic and old question...

There was a "format war" for ebooks (a "Tower of eBabel" for users)... EPUB won?
Wikipedia says that   «... EPUB format is the most widely supported vendor-independent XML-based (...) is supported by the largest number of e-Readers (...). The popularity of Amazon.com's Kindle devices in United States has led also to the prominence of KF8 and AZW » ... It is a truth for this "Ebook publishers and readers" community?

So, putting in other words:

  1. EPUB is a world-wide consensus? It is the most popular, for ebook readers today? We can put all money in this format?
  2. And about the "second place", what is the format? (PDF? MOBI?) This second format is still important for ebook-readers? There are reliable and updated statistics? (2010 example, 2009 example)


The question is about "Comercial + Public Domain" content.

For public libraries and public domain content the perception statistics are changing... People feel that there are "some standard" (EPUB?).

What we have heard (since 2009) in the comercial scenario is «PDF is still the format of choice for most people, though EPUB is getting respectable usage, with Mobi in third», but no reliable statistics about it.

To join "public domain scenario" with "comercial scenario" perhaps another kind of statistics must be also used: a survey like "ebook users read more comercial or public content?"

The world-wide statistics have distinct profile than USA-statistics, but most of the compiled data came from USA.

About replacement of the old and stiff PDF by EPUB, we have heard that "the market" is waiting the advent of HTML5 + CSS3-paged completion (be terminated and official W3C recommendations) and consolidation... How many years?

About reference numbers: how many ebook-titles user have (at Internet) in each format and each scenario?

  • Public domain and open content:

  • Comercial universe: ...? Amazon dominates?


3 Answers 3


First, a note: I will not be considering PDFs in this answer, because I do not consider PDFs to be ebooks. There are a number of reasons for this, like lack of reflowability and end-user customization options, but the primary reason is that PDFs are not generally sold at sites that sell ebooks--you can't sell your PDFs through iBooks or the Kindle store or whatnot. Others have other opinions, and that's fine—the relevant info is that I won't be considering PDFs here.

In terms of variety of devices supporting the format, epub is the clear standard—it's supported on nearly everything that reads ebooks. When you look at numbers, though, it's a different story: according to an article at Digital Book World, a recent Book Industry Study Group found the following statistics to the question "Where do you typically acquire ebooks?":

Amazon.com website: 51.3%
Amazon App: 15.7%
iBooks/iTunes (Apple): 8.2%
Barnes & Noble App: 6.1%
Barnes & Noble website: 5.7%
All other sources: 12.8%

This means that Amazon accounts for roughly 2/3 of the sales of ebooks, making their proprietary mobi/KF8 format the dominant format.

In essence, there is no "winner" yet, and there is not likely to be any time soon. Apple, Google, Barnes & Noble, and Kobo are enough to ensure that epub will remain alive and kicking for quite some time. With a majority of the sales, Amazon has no impetus to switch to a standard, and they don't appear to be in any danger of losing much market share. Where we are is where we're likely to be for quite a while, which means making two formats: epub and mobi/KF8. fortunately, Amazon has gotten much better at making tools that convert from epub to their format, so concentrating on epub will give you something for Amazon as well with little extra work.

  • 1
    Thanks, this is a good starting point (!)... But it is incomplete without public domain content, and without non-USA e-commerce statistics. Example: As of March 2014, Project Gutenberg claimed over 45,000 items in its collection (but not have any format-download statiscs); SciELO and many other minor public domain e-book projects are also distributing ebooks. Commented Aug 24, 2014 at 12:51
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    How about software support? As I read around, epub seems to be a much more popular format to create books (even if Kindle coverts it to mobi).
    – Greg
    Commented Aug 24, 2014 at 19:43
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    Epub is a much more popular way to create ebooks because Amazon's format is proprietary; you can't directly make it. You can only convert to it from epub or a few other formats.
    – Tom
    Commented Aug 24, 2014 at 20:33
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    @greg: 1000% agreed; that's why I don't ever buy books from Amazon. They're proprietary and terrible.
    – Tom
    Commented Aug 27, 2014 at 7:52
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    Sure, but given the option, why support a company that does stuff I don't approve of?
    – Tom
    Commented Sep 7, 2014 at 17:02

Amazon has over 2.8 million ebooks, including nearly all public domain books. See the left hand column, which provides an update to date count of ebooks available: http://www.amazon.com/s/ref=lp_154606011_ex_n_1?rh=n%3A133140011&bbn=133140011&ie=UTF8&qid=1410374478

This 2.8 million books makes things like Project Gutenberg statistically insignificant.

Your quote that "EPUB format is the most widely supported vendor-independent XML-based" is obviously designed to exclude MOBI/Kindle from the mix, because it's not vendor-independent. And sure, outside of Amazon, it is the dominant standard.

But more importantly, why do you want to know?

If the answer is because you want to know what format to publish a book in, versus you want to build an eReader app, versus you're writing a research paper, there are very different implications.

If you're an author publishing commercial fiction, since Amazon has about 65% of the ebook market, you must publish in MOBI to be successful. If you are an indie author, Amazon has an even bigger percentage of the market for indie authors (anecdotally 80+%), and so it becomes even more crucial.

If you are providing an ebook where access is crucial, e.g. a school text book that must be available to all students, then you must publish in both EPUB and MOBI.

Since EPUB and MOBI can be easily converted back and forth, one might argue that the question is irrelevant. Simply provide books in both formats.

  • Hum... a first point... I not know how write right English (I need help of web-translators), but "my book" can add "+1" at Kindle Store counter... By other hand, "my book" will never appear on Project Gutenberg. When we count "any thing" at Amazon we need to compare it with "any thing" at the full-Internet, not only with Gutenberg... Commented Sep 11, 2014 at 0:38
  • You cited discussions, not reliable sources of statistics... Forbes, that cite Newyorker.com, are good sources, but there are no newer result for @Tom's answer (your 65% is the "51.3%+15.7%" of Tom's). The BISG (Book Industry Study Group cited by Tom) report is good, so what is wrong or what is what's missing? BISG is an U.S. trade association, as Amazon; and Amazon, with others, with focus on non-public contents, was pay BISG to produce the report... Some good results found there, and perhaps other independent report confirm the same results... So, where the "other independent reports"? Commented Sep 11, 2014 at 14:05
  • Again, I will refer back to: What decision are you trying to make? What is the purpose of the question? Are you testifying in front of a judge? That requires a different level of reliability than say, trying to decide how and where to publish your novel. Commented Sep 11, 2014 at 23:19
  • We develop software and offer services for "content management/styling/transform"... Some software need a 2-year plan... What will the scenery in 2 years? How will the market and the "reading habits"? Our main customers are public domain content producers, for non-US readers... This is our reality, and is the same for many middle/small company around non-US-world. Commented Sep 12, 2014 at 0:38
  • If that's your need, then it's a complete non-issue. Decide on a base platform (and personally, I think EPUB is the one to use) and then convert to the other for distribution to nearly 100% of the market.
    – Auspex
    Commented Sep 16, 2014 at 0:58

   This is a Wiki, please edit and collabore! We need good English and updated content.


As used here:

  • e-book and e-book reader: e-book is the content, a file; and the e-reader is the device, a hardware (or software+hardware). Sometimes the content (e.g. CSS or Javascript code) have some algorithmic prescriptions for e-reader.

    • e-reader: considering here that an e-reader is a "paper substitute" device, so a Desktop PC computer or an iPhone are not dedicated e-readers, but Kindle and a Tablet computer are.
  • "usable e-book format": in a broader sense, paper-oriented formats, like PostScript or PDF, are acceptable for e-books, and can be called e-book formats.

  • real, strict sense e-book format: neither a "web format", like HTML, nor a "paper format", like PDF. The e-Books are "paged media", as paper books, but with diagramming flexibility: an e-book need to be reflowable, a resizable content that adapts to different resolutions and different aspect-radio screens.
    PS: generic HTML is not an ebook format because is not "all in only one file", but sometimes (e.g. using inline SVG and base64-encoded PNG images) HTML can be adapted for it.

  • "interactive e-book format": another growing demand for e-books are interactivity (EPUB example ), but we can ignore this demand here, in favor of the strict sense, and the necessity of classic books into digital devices.

So, conceptually, PDF is considered an (usable) e-book format because it is a legacy from old paper-oriented systems, where authors and layout designers were oriented to the paper size. As of 2012 the screen of the "e-book reader" is the final recipient of the content, and layout authoring is oriented to (some) screen adaptability.

There are three important criteria — metrics to check if a format is de facto standard — for electing e-book format popularity:

  • most widely supported formats: between popular e-book readers, statistics about direct support (without content loss or conversion demand) for each format.

  • more downloads: sales and download counting, in reliable "sales statistics" at bookstores and download statistics at libraries.

  • availability: number of distinct online links (at online libraries and others), each link to a distinct file download of a public domain e-book. Example: number of titles into the Project, SciELO, etc.

New results in 2020?

... Please collabore...

Old results in 2012

Supposing reliable information (see sources),

  • supported formats (by tablets plus strict e-readers): PDF and EPUB. I kick around ~90% PDF, ~80% EPUB.
  • downloads (only e-book sales, global): PDF, EPUB and (only USA market) MOBI. I kick around ~50% PDF, ~40% EPUB.
  • availability (only public domain e-books): PDF and EPUB. I kick around ~90% PDF and TXT, only ~10% EPUB.


  • if my software problem is "what e-book formats to offer", I need to check my public. For non-USA public, EPUB is the only format. For USA public, EPUB and MOBI.
    NOTE: it is for "e-book demand", but, check your public and their necessities. Nowadays, a printed book is also a necessity, people still like to use paper. PDF (with adequate paper size) may be a good option for generic (paper plus e-book) demands.

  • if my problem is "what e-book formats to accept" (ex. Receiving e-books to build a library), there are more options, and some conversion problems to solve with software.

  • if there are no software problem, is only to say "the standard is" or "the most popular is". You can say: "the most disponible is PDF", "the most acceptable are PDF and EPUB", and, in strict sense, EPUB is the most popular, the de facto standard e-book format.


(Please edit here to correct or to add more sources)

Supposed to reliable/medium/informal sources by context (formal/informal), databases (general/strict), etc.

1 - Reliable sources

1.1. Wikipedia Comparison of e-book formats: show that EPUB and PDF are the most widely supported formats.

1.2. Indicated as reliable by Wikipedia at market share information:

1.2.1. Goldman Sachs 2010 report cited by Quantity market shares of e-book sales in US: with Amazon (58%) and Barnes&Noble (27%) dominating. Amazon offers MOBI, the others EPUB.

1.2.2. Market share of e-readers in Canada by Ipsos Reid at January 2012: Kobo 46% (EPUB), Amazon 24% (MOBI) and Sony 18% (EPUB) dominating.

1.3. With sources cited by Wikipedia, at Tablet computer, "As of October 2012, the top-selling tablet is Apple's iPad with 100 million units sold, (...) followed by Amazon's Kindle Fire with 7 million, Barnes and Noble's Nook 5 million, and Google's Nexus 7 with 3 million units.": Apple, Nook and Nexus are EPUB, so EPUB represent more than 95% of Tablet market (and MOBI less than 5%).

1.4. SciELO Library: in November 2012 there were 377772 (378 thousand) articles in PDF and EPUB format.

2 - Informal sources

2.1. Project Gutenberg Library: over 40000 (40 thousand) books in TXT, and less into other formats, including EPUB and MOBI.

2.2. Smashwords bookstore 2010 statistics: counting selling/download, 35% PDF, 22% EPUB, 15% MOBI, 9% TXT.

2.3. O'Reilly bookstore 2009 statistic: shows PDF and EPUB dominating.

2.4. Manybooks bookstore online statistics, counting since 2009: PDF (24%), EPUB (22%) and MOBI (10%) dominate.

 (initial content adapted from SO)

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