Best eBook format for eReader


An ePUB (electronic publication) is an open standard format for eBooks which is created by the International Digital Publishing Forum (IDPF), a global trade and standards organization. As an open standard, it is compatible across a wide range of eReaders and has become the universal standard for ebooks. An ePUB renders text and content specifically designed as reflowable content allowing the user to control the size of the text as well as make use of other features such as highlighting and bookmarking. Links and rich media can be added to ePUBs.

Most eReaders or reading app on the market like Nook (Barnes & Noble), Apple's iBooks, Kobo, Adobe Digital Editions, Google books on Android, etc all supports EPUB files. 

Like an HTML website, EPUB format supports inline raster and vector images, metadata, and CSS styling.

- Displays text in a flowing manner—meaning, when you zoom the text in, it will fit on the screen or the size and layout will adjust to whatever the size of your screen. This best applies when using portable devices such as tablets and smartphones 
- Smooth reading – when words fit correctly in your screen, it will be much easier to read. All you have to do is scroll up and down or just flip pages 
- Can be read by several devices like the famous Apple products (iPad, iPhone, iPod Touch) and Android devices 
- Is the widely preferred format for those seeking to innovate their content. However, ebooks that have been published in PDF may still be upgraded to enhanced ebooks. Publishers only need to convert PDF to EPUB and then add more multimedia features. 

- Kindle does not read EPUB files 


MOBI is basically Amazon’s eBook version of ePub. There is not much difference between an Epub and a MOBI file. It’s just that MOBI file format is designed for Kindle. A file with .mobi extension is originally developed for MobiPocket Reader. It's another open standard for eBook publishing. It was purchased by Amazon later. It's based on an open-standard eBook format using XHTML and JavaScript. It's also cross-platform, eBook in this format can have .prc or .mobi extension. 

Images in mobi eBooks are limited to a 64 KB size. It contains advanced navigation controls and supports file compression, indexing, and dictionaries. 

- Smooth reading and flowable text 
- If you’re planning to sell your book in Amazon, this is the perfect format 

- Cannot be read on a device that doesn’t support MOBI files 
- If you’re using Kindle, you have no choice but to buy books from the Amazon store 
- MOBI files are sometimes large in size 

EPUB vs Mobi

We can easily convert EPUB to other eBook formats. It's supported by variety of platforms except Amazon Kindle. While Mobi is only readable on Amazon device or reading app. 

Currently, most of Mobi files are usually DRM free, because Amazon will change Mobi to AZW once it's protected by DRM. EPUB files can be locked by 3 main DRM schemes on the market, including Adobe DRM, Nook DRM and Apple FairPlay DRM. This prevents the files being printed, copied, etc. 

File Size
The file size for Mobi and EPUB formats can be different. EPUB file is much smaller than Mobi. If we download the same eBook for both EPUB and Mobi format, Mobi file can be the 2 times the size of EPUB file. 

Both Mobi and EPUB can display reflowable content and fixed width layout.

EPUB file can adjust itself to the size of screen. Because of the image size limitation of 64K, Mobi formats are suited for smaller screens.


AZW is a proprietary format developed by Amazon specifically for the Kindle eBook reader. It has its roots in the MOBI format but has better compression and encryption apart from a few more changes. The AZW format has found its place in many platforms with Kindle reading apps apart from Kindle. But AZW files can only be obtained from the Amazon online bookstore.

AZW format is DRM (Digital Rights Management) restricted and is locked to the device id which is registered automatically with the user account of the Kindle purchaser. But DRM free books also carry the AZW extension but they are really no different from MOBI files.


Now that we know what MOBI, EPUB and AZW are, we can easily analyze their differences:

MOBI, EPUB and AZW eBook formats all support DRM and all of these formats are available through different vendors on the internet but only the AZW eBook format is strictly supports DRM. MOBI and EPUB eBooks have optional DRM and are available or can be created DRM free.

EPUB is an open format, so it is available freely and also through vendors with DRM like Apple iTunes, Google Play Books, Barnes and Noble. MOBI and AZW formats are both of Amazon so they are available in Amazon’s Kindle store and are supported by Kindle eBook readers. AZW being Amazon’s proprietary format, is only available in the Kindle Store.

All three formats support reflowable content. But only in MOBI and AZW eBook formats, people can draw and add annotations on the eBooks. EPUB does not support these functions, but users can do this on different apps and softwares.

EPUB and MOBI eBook formats can be viewed almost on all major operating systems like Windows, Linux, Mac, Android and iOS. AZW is strictly accessible on Amazon’s Kindle Store and Kindle eBook readers and desktop eBook reader.

EPUB is an open standard format maintained by the International Digital Publishing Forum (IDPF), whereas the MOBI and AZW formats are proprietary formats and owned by Amazon.

MOBI was bought by Amazon and the AZW format is a modification of the MOBI format.


A PDF (Portable Document Format) is a digital, universal file format used to represent and share documents across multiple operating systems and devices. When a file is converted into a PDF, it looks like a digital photocopy of the original by retaining its fixed layout, fonts and graphics. A PDF can also include clickable links, form fields and audio video. Virtually anyone can read a PDF using free Adobe Reader software.

Pros of PDFs

PDF is currently the most widely used electronic document format worldwide. There are a lot of advantages to working in PDF format. PDF files give you control over layout and fonts.

They can be generated by GUI-based tools from a number of companies beyond Adobe. For example, Microsoft Word has the ability to produce PDF files. The reader software is free and comes installed on most computers.

Cons of PDFs

Code to generate PDF files is complex and, from a software developer’s point of view, difficult to master. Conversion of PDF files to a web-friendly format is difficult as well. PDF files are not easily reflowable. In other words, PDF files don’t adapt well to various sized displays and devices. It is difficult to view some PDF files on small screens that come with some readers and smartphones.


HTML (HyperText Markup Language) is the programming code used to build and render pages on the World Wide Web. HTML uses tags to provide a web browser with the directions on how to structure and present a web’s text, graphics, layout and links. The content is re-flowable and re-sizable by the user. Virtually anyone can read an HTML page with a web browser.

HTML vs ePub

HTML was invented in the scientific sector and it missed the class on business reasoning. No digital rights management you will say, no "big guns" supporting the business case, no sales channels no nothing. Just a format to distribute content. But it does that very well and it is at the base of many great content related businesses right now and in the visible future (let's just mention the web itself and the social network phenomenon). What will all those be without HTML? 

EPUB on the other hand has all of the above. It offers DRM (actually the Reader/App that interacts with it offers it but that is a different story) ... It comes with the backing of all major publishers ... It has multiple sales channels (very real web shops selling books in this format) and we might find some other advantages.

Uniformity of display: the strictly defined tags that are the backbone of a EPUB file (well, the XHTML that makes up the EPUB file) allows for consistent display on any device. If you want your image to look a certain way no matter where it’s seen, the EPUB standard gets you a lot closer to that than standard HTML. Same deal with the strictly defined CSS subset.

Metadata: librarians and booksellers rejoice! EPUB files package metadata within the file itself (just like those other reading devices, hardcovers and paperbacks).

Ability to specify contents and reading order: internal reference and order are simple to specify using the OPF specification…and it’s easier and more user-friendly than just inline HTML.

DRM-possible: yes, it’s true that it’s easier to apply DRM to EPUB than to HTML. Using these files allows the option to be there if that’s the route the publisher wants to take.

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