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A Beginner's Guide to's Ebook Formats
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A Beginner’s Guide to’s EBook Formats

By Masha du Toit

This article is aimed at writers who want to understand the ebook formats used by Amazon KDP. This is not a tutorial on how to format an ebook but a guide to the basics of ebook formats. This will help you understand what the person who formats your book is doing, and help you check whether their work is up to spec. You will find information on:

The parts of a typical ebook

There is quite a lot of variation in how ebooks are structured. Some ebook are compressed folders that contain the various documents that make up the ebook. Other formats are database files that contain this information. In most cases, an ebook will be made up of:

For example, here is an example of the parts of a typical ePub book with its folder structure expanded to show its contents:

Where do these come from? Must I create them? Can I see them?

The CSS, TOCs, XHTML and OPF documents are created during the formatting process. You will find a description of some of the typical formatting processes at the end of this document.

Whether you can see these various parts depends on the format. If the ebook is in the ePub format it is relatively simple to unpack and see these aspects of the book. Any changes to an ePub can be done with ePub editing software such as Sigil. If the book is in the Mobi format then it is not so straightforward to edit it. A Mobi file cannot be easily unpacked and edited. In most cases, if there is a problem with a Mobi book, the formatter will have to recreate the Mobi file from the original text document again.

A closer look at the “table of contents”

There is some confusion around the topic of tables of content (TOCs) in ebooks. You may have noticed that there are two TOCs  in the above list: the “linked toc” and the “logical” toc.  

The linked TOC

TOC.html is the “linked table of contents”. It appears as a page in the book, usually near the front. The person reading sees it as a list of chapter headings. The reader can click on these links to navigate to a chapter. It is also possible for the reader to find the linked TOC by using the Go To > Table of contents command on the reading device. Here is a screenshot of a typical linked TOC as it appears on a Kindle 3:

The logical TOC

The other TOC document, TOC.nxc is the “logical TOC” also called the “navigational TOC” . This is the part that is responsible for those little dots on the progress bar at the bottom of the book, or for the “time to read chapter” feature on a Kindle Paper White.

These little dots are very useful to a person reading the book. They make it possible for the reader to skip forward or backward one chapter at a time at the press of a button. Here is a screenshot of the dots on the progress bar on a Kindle 3:

If the book does not have a logical TOC, the progress bar looks something like the screenshot below. There are no dots, so the person reading the book cannot use the kindle controls to easily skip forwards or backwards between chapters:

How are the TOCs created?

The logical TOC is created when the book is formatted. The linked TOC can be created by you in Word or whatever editor you are using, or it can be generated when the book is formatted.

For the either of these TOCs to be generated during formatting, each chapter heading must be set to a particular style (e.g. “heading 2”). The conversion software is instructed that all “heading 2” headings are chapter headings. It can then create both the logical and linked TOC based on that information - or if you have created the linked TOC already, only the logical TOC will be generated.

Amazon KDP TOC guidelines

Ideally your book should contain both a linked and a logical TOC. The official Amazon KDP guidelines “strongly recommend” that you have both kinds. Up to now, KDP has accepted books that lack these but if a reader complains, you may receive a note from Amazon that your book lacks a table of contents. This can be confusing if you already have a linked TOC and do not realise there is also another kind, the “logical” TOC.

According to KDP guidelines:

But what if I write fiction? Do I need a TOC?

There has been a lot of discussion around the question of whether or not fiction books should include a TOC. Some writers feel they are unnecessary, unattractive, or needlessly take up space in the sample.

You will have to make up your own mind about this but take the following into considerations:

Cover Images

Creating an eye-catching cover that will help readers decide to choose your book is a highly specialised skill. I’m not going to discuss how to create a good cover, but just go over the technicalities of book cover images.

There are two versions of the cover: an “internal” cover that is part of the book file, and an image that will be uploaded as a separate document to Amazon Kindle Direct, and will become the cover image on your book’s page on Amazon. I’m calling that image the “external” cover, as far as I know there is no official term for this type of cover image.

You can use the same image file for both the internal and external cover. It is also possible to use different versions of the cover for each of these - for example, you may choose to use a smaller version for the internal cover. As long as both files display the same image! :)

It is important to note that the cover image should not be inserted into the document you used to write the book. For example, if you wrote the book in Word, the cover image must not be inserted in that Word document. This can result in the book having two cover images, which is not ideal. The image you choose for the book’s cover will be turned into an internal cover by the person formatting the book. They will insert the image into the book file during formatting, along with the necessary coding to ensure that the Kindle reader recognises the image as the book’s cover image.

The technical specifications for the external cover image (the one that will be uploaded along with the book) are:

Also be aware that according to the Amazon KDP guidelines, the cover may not:


What formats are there?

There are many ebook formats. You are most likely to come across Mobi or ePub. These two formats are very similar in the way they are structured. Their underlying technology is almost identical. Despite that, there are distinct difference between Mobi and ePub books in terms of where you get them from and what devices you need to read them on.

Mobi is best known for its association with, but you can buy Mobi ebooks from other ebook sellers as well, e.g. Smashwords or Feedbooks. If you are preparing a book for Amazon Kindle Direct, you will most probably need to create a Mobi formatted book. You can read Mobi books on any of Amazon’s Kindle e-readers. You can also read Mobi files on e-readers such as the Kobo Reader, or on your desktop computer, tablet computer or smartphone with the correct application installed.

 A close relative of the Mobi is the Prc which is essentially the same as a Mobi in this context.

ePub is one of the most widely used formats. Many sites such as, for example Kobo, provide their ebooks in the ePub format. Many e-readers can read the ePub as well as any computer, tablet computer or smartphone with the correct applications installed.

You cannot read ePub books on any of the Amazon Kindles, except of they are presented in Amazon’s own “kf8” format, and even then, only on the Kindle Fire, or fourth generation Kindles with the correct firmware.

What is .azw, .prc or kf8?

You may have noticed that some books you download from Amazon have the file extension “.azw” or “.prc” or “kf8”, and some have the file extension “.Mobi”

In the context of ebooks, a .prc file is a .mobi file. The ebook reading devices handle them in pretty much the same way. You can change the file extension from “prc” to “mobi” and it will make no difference to how the file works.

An .azw file is’s proprietary version of the Mobi format.

A .kf8 is’s proprietary version of the ePub

What formats can you upload to KDP?

There is a difference between which formats you can upload, and which you should upload :)

You can submit your book to KDP in a number of formats which the KDP software will convert to a book that can (hopefully) be viewed on a Kindle.

You can upload

But beware! Not all formats are created equal. The more the file you upload has to be changed by Amazon’s conversion software, the more likely there will be problems with the book. For example PDFs are notorious for turning into nasty looking ebooks that contain strange page breaks, page numbers and other unwanted elements. Uploading a Word or an HTML document is possible, but it is impossible to predict how these will work when viewed on some of the newer Kindle devices like the Kindle Fire.

What is the best format to use?

Ideally, you (or the person formatting your book) will turn the book into a format that is as close as possible to that used by Amazon, so that no unexpected surprises happen during conversion. Of the above list, the most likely contenders are Mobi and ePub.

In addition to this, an advantage of using a Mobi file is that you can test it on a Kindle device or on Kindle Previewing software before uploading the book to Amazon. In this way you can really be sure that it works properly before it becomes available for sale or download.

But...why can’t I just upload the Word document directly to KDP?

While you can upload Word documents, it is becoming increasingly likely that the resulting ebook will contain errors. This is because Word is not set up for ebook creation. It introduces a large amount of unnecessary code into the book file. At the time of writing, there is an error called the “Paperwhite Bug”. This bug means that many Kindle documents that were created in Word display incorrectly on the Kindle Paperwhite. The font size is almost unreadably small and cannot be changed and in some cases the incorrect font type is used. The reason this happens is because Word specifies font size as “points” instead of “ems” or “%”, which is the unit of measurement an e-reader requires.

Even if your book looks fine at the moment, there is no guarantee that it will display correctly on new generation e-readers. The best way to “future proof” your book is to submit it as a well crafted ebook format such as ePub or Mobi.

Do I need to provide all these different formats for the different devices?

There are many different types of ereaders out there, all of them needing different formats. Is it up to you to provide those? No. Amazon KDP will take whatever document you upload and convert it to the necessary formats those devices need.

But while you don’t need to upload the different formats, you do need to ensure that the document you upload can be faultlessly converted to those formats so that it works properly on all Kindles. This is the responsibility of the person doing the formatting. If the book is not formatted correctly, it may not work properly. It may not be possible for readers to change the font size, or the table of contents may be missing.

A side note: It is very useful to have your book available in a number of formats. You might want to send your book to a potential reviewer or simply give it to a friend, and they may ask you for a specific format. Having a copy of your book in Mobi as well as ePub should cover most bases.

How can I check that my book works on the various types of Kindles

One method to make sure your book is flawless (as far as the formatting is concerned anyway!) is to view your book on as many types of Kindle as you can get your hands on.

 If you do not have access to a Kindle, you can use the Kindle Previewer software. This software makes it possible for you to preview your book as it would look on the various types of Kindles. It is available from - note that there is a link to a user guide on that page.

How can I tell if a book is well formatted?

The best way is to look at the book on a Kindle device or to preview it using the Kindle previewing software mentioned earlier. Check for the following:

How to prepare your book for formatting

Even if you do not do the formatting yourself you can prepare your book document to ensure that the formatting process is as smooth and error free as possible. This is just a quick overview - you will find links to step-by-step tutorials at the end of this article.

A typical formatting workflow

You may never need to format a book yourself but it is worth knowing what the various stages are. You may need to do a small update to a book and if you understand the process the person formatting the book is using, that can help speed things up.

Some typical formatting workflows: Epub

Since ePub is an open source format, it is relatively easy to create. You can convert a document into the ePub format using conversion software, or you can use ePub editing software to create it from scratch. This means there are a number of possible work-flows.


Some typical formatting workflows: Mobi

Mobi: Unlike the ePub,you cannot “hand-build” a Mobi book. In other words, there is no software package that you can use to directly edit the Mobi file. Instead, you typically convert the book - using software such as KindleGen or Calibre - into the correct format.

It is not possible to make changes directly to a Mobi file. To fix errors or update the book, you will have to edit the source file - usually a Word or an HTML document, and then convert that to Mobi again.

So a typical Mobi formatting workflow might look like this:


Tutorial Links:

How to create a linked TOC in Word:

The Smashwords Style Guide: An explanation of how to prepare your book for uploading to Smashwords, but it is actually quite a good general guide for preparing a Word document that is to be converted to any kind of ebook format:

Guido Henkel’s guide to formatting with HTML and CSS using a text editor:


Amazon KDP’s Publishing Guidelines:

An overview of how to make a Kindle ebook:

MobileRead’s pages on the various formats:

Elizabeth Castro’s “ePub Straight to the Point”

A Beginner's Guide to's Ebook Formats by Masha du Toit is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Based on a work at