Learn About eBooks

eBook Formats

The eBook formats explained below are the most common ones you will run into when developing standard eBooks. While there are other proprietary formats, these are the formats used on the majority of eBook devices and sold by the major retailers. For a quick overview of the formats compared to each other, here is an easy comparison table.




Mobipocket – About This Format

Mobipocket is a French company that developed its eBook creation and reading software when eBooks were still in their infancy, and managed to flourish in the nascent market, eventually being purchased by Amazon in 2005. When Amazon decided to develop the Kindle, it was a logical step for the company to use its own proprietary format for the new device’s eBooks. The Mobipocket format is based loosely on HTML 3.2 and includes some unique formatting requirements.

Note: While Kindle devices can still read the Mobipocket format, it has been replaced in the eBook market by Kindle Format 8.

Mobipocket – Technical Specifications

DRM: The Mobipocket format allows books to be locked with Digital Rights Management (DRM) or not. When an encrypted file is downloaded from a retailer it is locked to the user’s registered device. The Kindle devices use the same DRM, but files bought from Amazon cannot be read in old Mobipocket reading applications.

Devices: Kindle eBooks can be read on any of the Kindle devices, as well as in any of the Kindle Apps.

Extensions: Mobipocket/Kindle files come in three different file extensions: .mobi, .prc, and .azw. There are no functional differences between these formats, and the files themselves are exactly the same.

Note: Joshua has written the most authoritative book on formatting books for the Kindle in the Mobipocket format. Check out our Kindle Formatting website for more information.

Mobipocket – When to Use

We do not recommend using the Mobipocket format for your eBooks. It is not as up-to-date as Kindle Format 8, and it has a lot of stylistic limitations that you do not have to worry about in the newer format.




KF8 – About This Format

Kindle Format 8 (KF8) was released by Amazon in late 2011. It is the successor to the old Mobipocket format, and has been updated to include a variety of new featues and functionality. KF8 has support for HTML5 and CSS3, and it also has a built-in fixed layout format that is especially well-suited for children’s eBooks.

KF8 – Technical Specifications

DRM: Kindle Format 8 allows books to be locked with Digital Rights Management (DRM) or not. When an encrypted file is downloaded from Amazon it is locked to the user’s Kindle device. This DRM cannot be applied by anyone except Amazon.

Devices: KF8 eBooks can be read on any of the Kindle devices, as well as in any of the Kindle Apps.

Extensions: Kindle files come in three different file extensions: .mobi, .prc, and .azw. There are no functional differences between these formats, and the files themselves are exactly the same.

KF8 – When to Use

While KF8 has many of the same features as ePub2 and ePub3, it is not the same. There are still some key differences between the formats, and we do recommend creating native Kindle files, not just auto-converting an ePub using an conversion tool like KindleGen.

KF8 files should be given to Amazon for sale in the Kindle store. They can also be sold on your own website.




ePub2 – About This Format

The ePub format was developed as an industry-wide standard for eBooks. It is based on a variety of other technologies and standards, like Open eBook and XHTML 1.1, but its uniqueness is in how it combines these standards to provide a solid formatting foundation for eBooks of just about every shape and size.

The ePub standard is maintained by the International Digital Publishing Forum (IDPF), a non-profit organization made up of technology and publishing companies. eBook Architects is an active member in the IDPF.

ePub2 was first introduced in 2007, and had a minor maintenance update in 2009. It is widely used by a large number of retailers, and is the most common eBook format used on the market. However, ePub3, the latest version of the ePub standard, is the format that most retailers are moving toward. It contains more enhanced functionality than ePub2, as well as a large number of important core updates.

ePub2 – Technical Specifications

Code: ePub2 files are built in XHTML 1.1 and CSS2. Some reading systems are able to handle the formatting better than others.

DRM: The most popular DRM option for ePub files is Adobe Content Server, which is utilized by Barnes & Noble, Sony, Kobo, and many other eBook stores. Apple’s iBooks application (on the iPad) utilizes Apple’s own Fairplay DRM, which is not compatible with any other eBook device or application.

Devices: ePub2 files can be read on most eBook devices in the market, with the exception of the Kindle platform.

Formatting: ePub2 files are natively reflowable. Apple created a fixed layout extension to ePub2 that is still widely used for children’s eBooks, but that is not part of the official ePub2 specification.

ePub2 – When to Use

ePub2 is the most common format for sale on the market. Most authors and publishers currently make ePub2 files, and all of the retailers except Amazon accept them. Amazon has even updated its KindleGen tool to better handle the automated conversion of ePub files.

ePub2 will continue to have solid support in the market for many years to come, so publishers and authors should feel comfortable developing in this format without fear that the files will stop working. The ePub3 specification even includes a requirement that reading systems support backwards compatibility for ePub2 files.

However, if you are able to move to ePub3, we do recommend making the switch. If you add in some backwards compatibility for devices that do not yet support the ePub3 format, then you can sell ePub3 files on most of the major retailers.




ePub3 – About This Format

ePub3 is the latest version of the ePub format. The ePub standard is maintained by the International Digital Publishing Forum (IDPF), a non-profit organization made up of technology and publishing companies.

ePub3 was released in 2011, and has been gaining traction in the marketplace since that time. It is currently officially supported on only a few reading systems, but it can be ingested by most of the eBook retailers.

ePub3 was updated to include better support for foreign languages, embedded media, and other core features and enhancements. It also has a fixed layout formatting option that is beginning to be adopted for children’s eBooks and even for non-fiction titles.

ePub3 – Technical Specifications

Code: ePub3 files are built with XHTML5 and CSS3, along with some special styling options that are unique to the ePub standard.

DRM: The most popular DRM option for ePub files is Adobe Content Server, which is utilized by Barnes & Noble, Sony, Kobo, and many other eBook stores. Apple’s iBooks application (on the iPad) utilizes Apple’s own Fairplay DRM, which is not compatible with any other eBook device or application.

Devices: ePub3 files are best supported in iBooks, but they can also be read in other reading systems.

Formatting: ePub3 files are natively reflowable, but there is also a fixed layout option that can be used for children’s eBooks and non-fiction fixed layout eBooks.

ePub3 – When to Use

ePub3 is becoming a more accepted standard, and more retailers are starting to sell them. However, there are some pitfalls to using ePub3 files, and we highly recommend testing them extensively before you put them up for sale.

For information on what devices support the various features in ePub3, take a look at the BISG ePub3 Support Grid.

Nook Kids



ePib – About This Format

“ePib” is the unofficial name of the NOOK Kids format. This is a fixed layout format that is only used for children’s eBooks in the Barnes & Noble NOOK platform. It is not supported on other devices or platforms, and it is not possible to sell it from your own website.

While the file structure behind an “ePib” file is similar to that of an ePub file, the NOOK Kids format is dramatically different in many ways. These files are created from PDF files, not HTML and CSS, and the resulting code is not editable or able to be enhanced. NOOK Kids files are built with a proprietary tool that is only available to publishers with a direct account with Barnes & Noble; these files cannot be sold through the NOOK Press self-publishing portal, so you must have a publisher account or use a distributor to sell them.

The NOOK Kids format has a few useful features like audio narration and region magnification, but it does not allow embedded video, page zooming, or other features that are available in other children’s eBook formats. For more information, please see our Children’s eBooks page.

ePib – Technical Specifications

Code: NOOK Kids files are built in a proprietary tool with a PDF file or page images as the base content.

DRM: B&N applies their standard Adobe DRM to these files at ingestion.

Devices: NOOK Kids files can only be read in the NOOK tablets and in certain NOOK applications for devices like the iPad.

Formatting: This is a fixed layout format designed specifically for children’s eBooks. It is not an appropriate format for non-fiction or other kinds of content.

ePib – When to Use

The NOOK Kids format is necessary for selling Children’s eBooks on the NOOK store. We highly recommend that you create this file in addition to the fixed layout ePub2/ePub3 and Kindle Format 8 files for your children’s eBook.



iBooks Author

iBook – About This Format

iBooks Author is a proprietary eBook format created by Apple and intended for complex non-fiction eBooks like textbooks, cookbooks, etc. The iBooks Author format is only able to be read in the iBooks ecosystem, and it can only be created in the iBooks Author program on a Macintosh computer.

iBooks Author files are inherently fixed layout, meaning that the design is static and does not allow the reader to change the font size or other visual settings. However, iBooks Author also has an option for creating a reflowable version of the content that can be accessed by changing the orientation of the device. Normally the fixed layout design is implemented in landscape while the reflowable design is implemented in portrait, but this can be determined by the designer creating the file.

iBooks Author files should not be used for children’s eBooks because it does not have support for narration overlays (the Read Aloud function that is available in standard children’s fixed layout eBooks for Apple).

Apple calls these files “multi-touch” because they are designed to include interactive features and content, such as video, audio, and widgets. The format is also structured in a very consistent way for every eBook, with the chapters and each page within those chapters easily accessible.

While iBooks Author files are similar to ePub files in structure, they are not the same format and are not interchangeable with ePub files. In addition, iBooks Author widgets are built in Dashcode, which is mainly used to make widgets for on Macintosh computers. While Dashcode widgets can be built in a variety of ways, they will not always be easily usable in other eBook formats or devices.

iBook – Technical Specifications

Code: iBooks Author files are built in a proprietary tool. The code is essentially HTML, CSS, and JavaScript, but that code is not editable by the creator.

DRM: iBooks Author files do not have built-in DRM, but the FairPlay DRM can be applied by Apple when the file is sold in the iBookstore.

Devices: iBooks Author files can only be read in the iBooks application on its supported devices.

Formatting: Fixed layout is the default design option for iBooks Author files, and most books will be designed in fixed layout. The reflowable option in iBooks Author files is mainly used as a backup that allows a fast overview of the book contents.

iBook – When to Use

Apple recommends that all non-fiction fixed layout files sold in the iBookstore be made with iBooks Author. Many clients have also told us that Apple will not promote non-fiction fixed layout titles in the standard format, but will instead recommend using iBooks Author.

Because of this, we highly recommend that anyone considering making a non-fiction fixed layout file consider making the Apple version in iBooks Author. It is important, however, to use the format to its best abilities, so don’t just make your eBook a flat representation of the print design. Add some widgets, additional photos, more content, etc., and make the content really shine.




PDF – About This Format

PDF is very common document format. While most people will use Adobe products like InDesign or Acrobat to generate PDF files, there are a variety of other programs that can create PDF files, including some that install on your computer like a printer allowing you to “print” a PDF from almost any application.

The main problem PDF files have in the modern eBook world is that the text in PDF files cannot reflow to fit small screens. eBook devices like the Kindle and Nook, as well as phones and tablets like the iPhone, iPad, and Kindle Fire, all have screens that are smaller than a typical computer screen or even than a standard print book. As a result, when a PDF file is loaded on such a device it usually needs to be zoomed in to be readable, forcing the user to scroll left and right to be able to read all of the text on a line. This is why most eBooks formats like ePub and Kindle are reflowable.

In addition to this, PDF files are not sold by any of the standard retailers, so it is difficult to distribute them to consumers unless you are selling them on your own website.

PDF – Technical Specifications

Code: PDF files are not built in HTML. They are created with proprietary code and must usually be edited in the original source file.

DRM: PDF files can be encrypted with Adobe Content Server or they can have a password applied.

Devices: PDF files can be read on most eBook devices in the market, but none of the eBook retailers will sell a PDF to consumers.

PDF – When to Use

We do not recommend trying to sell eBooks in PDF format unless you are going to have that set up on your own website. Most consumers will recognize the PDF format, but usability suffers a lot when you place a PDF on an eBook device, and some systems will try to auto-convert the file when it is loaded, making the use of ePub and Kindle formats a better option. PDFs do work well for worksheets and other information that you think your readers should print out or view on their computer to accompany the eBook content.

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Is it a good idea to put my Table of contents at the end of my eBook?

Some people do this to increase the size of the free samples automatically generated by the eBook retailers. However, the Kindle and other devices will re-set the “last read location” to the end of the book if you have your Table of Contents there, so we normally recommend against that practice.

What is the difference between HTML5 and XHTML5?

HTML5 is the latest version of the HTML standard used on the Web and in eBooks. XHTML5 is a stricter and cleaner version of HTML5, with rules from XML imposed on the code. For example, when a tag is opened it has to be closed, and all of the tags have to be properly nested. XHTML5 allows the code to be more easily interpreted by the display engine, and it keeps the code more consistent and easier to edit.

I have heard you can’t use color in eBooks. Is that correct?

No, that is absolutely incorrect. eBooks look great with color, and we highly recommend using color images and even colored text (within reason) in your eBook files. Some devices have grayscale eInk screens, so the color will not show up on those devices. However, the color will be in the file, and it will work on all of the color devices. We do recommend you test colored text on a device with an eInk screen and ensure that the text will not be too light to read.

Do you need to have a separate ISBN for each version of the eBook for different companies?

Technically, yes. See an extended answer on our ISBNs page.

What is KindleGen?

KindleGen is Amazon’s eBook creation/compiling program. It is used on the KDP website to auto-convert files uploaded into the Kindle store, and it is also integrated into the Kindle Previewer program to handle the conversion of non-Kindle files loaded in that program. You can download KindleGen and get access to other Kindle creation information at amazon.com/kindlepublishing.

What is a fixed layout eBook?

Fixed Layout eBooks are HTML-based eBook files that are usually designed to match the layout of a print book. The key difference between fixed layout files and reflowable files is that reflowable eBooks allow the reader to have more control over the reading experience, such as changing the font size, background color, etc. For more information, please see our Fixed Layout Children’s and Non-Fiction pages.

Does Amazon sell HTML files or only Kindle?

Amazon only sells eBooks in the Kindle format, but that format, just like ePub, is built using HTML and CSS files.

How is fixed layout different from a pdf of the book?

Fixed layout eBooks are built using HTML, so they have more functionality than PDF files. For example, the narration overlay functionality used in many children’s eBooks is not possible in PDF files. In addition, none of the eBook retailers sell PDFs, so fixed layout eBook files offer the best sales opportunities.

A university librarian told me they are not acquiring any Kindle books but only HTML5/ePub. Have you found that to be common with other libraries? I know our local public library does buy Kindle books.

Libraries acquire their eBooks from services like 3M and Overdrive. These services sometimes offer an option for Kindle checkouts, but typically they are limited to ePub files because of the more common use of the Adobe DRM.

Has the Kindle format gotten any more sophisticated in how it handles tables or floating images?

Yes, Amazon’s Kindle Format 8 has support for many great design features, including floating images, tables, color text, embedded fonts, and more.

How are page numbers handled in an eBook?

Print book page numbers are included in the HTML code of both the Kindle and ePub formats as anchors. They are also listed in the PageList section of the NCX or Navigation file. The PageList is used by some reading systems (like the Kindle and iBooks) to show the reader the print page numbers of the book as they read.

How are page headers created in eBook files?

The different reading systems control what shows up in the header of your eBook. Most will display the title of the book, and some will also display the author name. That text cannot currently be set to display the chapter name or other information about where the reader is currently reading in the text.

How do eBooks handle hyphenation of long words?

Some eBook reading systems will apply hyphenation to longer words to make the text better fit on the screen. This is typically controlled by the reading system, and will change depending on the font size and other settings the reader has set on their device.

What about protecting the file?

eBook file protection is called Digital Rights Management (DRM). Please see our DRM page for information on how it works and suggestions on how to use it.

Can I sell my eBooks on my own website?

Yes! You are certainly able to sell your eBooks on your own website. For more information, please see this page.