A question that many readers ask is: What is the best format for Kindle? The best formats are: 1) directly compatible with the Kindle without the need for conversion; 2) fluid; 3) have rich formatting support. Let’s take a look at the different formats and choose the winner (or just skip to the end of the article to find out the winner):
Best formats are directly compatible with the Kindle. They are: AZW, AZW1, AZW3, DRM-free Mobipocket (MOBI, PRC), TXT and PDF. You can copy files in these formats directly to your Kindle using a USB cable and start reading. Or, you can email them to your Send to Kindle email address, if you don’t want to use USB transfer.
Also natively supported are Audible audiobooks (.AA, .AAX) and MP3 sound files (.MP3).
Second best are formats supported by the Amazon Kindle email conversion (Kindle Personal Documents Service). They are: HTML, HTM, DOC, DOCX, RTF, JPEG, GIF, PNG and BMP. You can email files in these formats to your Send to Kindle email address, Amazon will convert them into AZW3 automatically and send they will appear on your device.
Finally, there are formats that require third party conversion to be read on the Kindle. The most popular of these is EPUB.
Layout and Formatting
The second most important feature is formatting and layout. The best are so-called fluid formats – EPUB and MOBI, where free flowing text adapts to the screen size. These formats support links, tables of contents, and rich formatting. The new EPUB3 even supports multimedia – audio and video embedded in an ebook.
For comparison, PDF files are rigid – they are formatted so that each page is like a snapshot. Reading a PDF on a large computer screen is fine, but on a small Kindle screen PDFs are hard to read. Another comparison: a simple text file (TXT) format is not rigid and reflows, but it cannot have links, pictures, or any rich formatting.
Kindle File Format Details
AZW3, AZW1 and AZW
Any ebook retrieved from the Kindle Store comes in Amazon’s default proprietary format – AZW3 (this used to be AZW). This ebook format is exclusive to Amazon.com, and allows authors and publishers to apply copyright protection to their e-books in order to prevent unauthorized copying. The AZW3 file format supports rich text formatting, tables of contents with links, illustrations, etc.
DRM-free Mobipocket (MOBI, PRC)
Mobi was developed by the MobiReader company, which was later acquired by Amazon. Amazon used MOBI as the basis for their first AZW Kinlde format. The Kindle is fully compatible with DRM-free MOBI. This format can contain illustrations, links and rich text formatting. DRM protected files (with exception of ebooks purchased on Amazon) cannot be read on a Kindle, unless DRM is first removed. MOBI is what you would convert EPUB files to, in order to read them on your Kindle, and EPUB is the most popular ebook file format today (more on this in the EPUB section below).
PRC is essentially the same as MOBI. A PRC file is actually a container that can contain data in any format, including Mobipocket. Old Mobipocket ebooks were always in PRC, while the newer ones can have either MOBI or PRC as their extension. Any ereader that can read MOBI can read PRC as well.
TXT is a plain text format fully compatible with the Kindle. TXT is compatible with most digital gadgets and has a very small file size. The disadvantage is that TXT is limited to displaying plain text. Rich text formatting, links or illustrations cannot be embedded into a TXT file.
Adobe’s Portable Document Format, PDF was developed in 1993 as a digital document standard. It is readable on most electronic devices, and Kindle supports PDF directly. However, PDF does not reflow, so reading a PDF is like reading a photo. PDF is more suited for formulas, illustrations, and less for novels.
PDF files can be converted to the AZW3 Kindle ebook format in order to take advantage of variable font size and annotations. To have a document converted to AZW3, the subject line of your Send-to-Kindle email should be “convert”.
HTML (Hyper Text Markup Language) is a language used to describe web pages for web browsers to interpret. It is a very popular, widely-supported, open publishing standard. In fact, EPUB and MOBI are 99% HTML and CSS, plus some descriptive elements in XML-based files. Publishers choose EPUB and MOBI over HTML because digital books have specific requirements that HTML cannot satisfy.
DOC and DOCX are Microsoft Office document formats. Kindle supports them via the Send-to-Kindle email conversion.
JPEG, GIF, PNG and BMP
These four are image file formats most often used to display images on the Internet. They stand for: JPEG (Joint Photographic Experts Group), GIF (Graphics Interchange Format), PNG (Portable Network Graphics) and BMP (Windows bitmap).
EPUB (Electronic PUBlishing) is the world’s most popular format for electronic books, and many online libraries and bookstores offer books in this format. EPUB’s structure is similar to a Web page, packaged into an archive. Books in this format can have clickable table of contents, rich formatting and illustrations.
EPUB is supported by virtually all ereaders, except the Amazon Kindle. However, it can be converted into MOBI using software such as Calibre. Links, illustrations, rich formatting, etc. Everything will look the same after the conversion, because both of these formats are based on HTML.
Best Format for Kindle – And the Winner Is…
Based on our criteria, MOBI is the best format for Kindle. It is directly compatible, fluid, and it supports rich formatting. As a bonus, you can convert EPUB books from your library or online bookstores other than Amazon into MOBI, to read on your Kindle.
AZW3 is very similar to MOBI, but you cannot convert an EPUB file into AZW3 to read on the Kindle.