UPDATED 2022 article; this article supersedes and replaces the article that was published in  2015, titled “What is the Best eBook Format for Kindle,” which is still here on our site—seems to me that retaining historic information and data may be useful someday. Not sure when, mind you, but hey! Why not, right?

eBook Formats for KDP and other Vendors:

One of the questions that we are still asked, here in 2022, is, "what is the best eBook format for Kindle?” I'm not always sure what question I'm being asked.  Is the person asking to find out what file format they should upload to Amazon? Are they asking what's the best way to make a book for the Amazon-Kindle ecosystem? In 2010, those answers were easy.  Back then, the formats were:

  • ePUB: which stands for ePUBlication (clever, eh?), which is used by B&N, iBooks, Sony, KoboBooks, and Google, and,
  • MOBI format, which was, but no longer is, the preferred Kindle file format.

If you've Googled, you've likely seen all sorts of claims, ranging from some folks telling you that you can put an ePUB (directly) on a Kindle device, to the idea that using Word is the best "Kindle eBook format."

The bottom line is, as of midsummer 2021, the files that Amazon sells to its readers are, by and large, derived from the last-man-standing eBook format, which is ePUB. This does not mean that you can’t upload a Word file, still; you can.  But the process that used to intake a MOBI file, perform nominal conversions or changes to it and spit out a file that was optimized for the myriad Kindle devices, no  longer exists, at least, not for typical, everyday reflowable eBook files (your typical novel, memoir, self-help book, etc.)  Today, if you want to upload a reflowable eBook, you need ePUB format, not MOBI.

MOBI is still accepted, by Amazon, in certain special cases—those being for what are called Print Replica files (for example, heavy photography books or illustrated children’s books) where the placement of text and images is absolutely crucial and cannot be altered or “reflowed” as text does in regular eBooks when you change font size or screen size or rotate the device.  If you try to upload a MOBI file for a reflowable ebook, you’ll be stopped dead in your tracks.

History to some extent:

Now, if you've run across various forums, you may have seen people refer to AZW format, or AZW3 format. The former (was/is) the actual, final, encrypted Kindle format that is dispensed from the Amazon store, to your Kindle as a purchased book. That's not a format that you can make yourself. And, even if you could, you can't upload that format at the KDP, the Kindle Digital Publishing platform. The latter, AZW3, is a file format, created to emulate what's called "KF8," (the more-advanced Kindle formatting) by a piece of free library software called Calibre. However, just like AZW, you can't upload an AZW3 file format at the KDP. You can certainly make a file in that format, and side-load it to your own Kindle device, but you can't publish it. Obviously, that format, then, lacks utility.  Fine for personal use, but useless for publishing.  If someone starts yammering away at you, talking about how you can convert your file to AZW or AZW3 format, for the purposes of publishing--that's not someone to whom you should be listening. Not if you wish to publish at KDP.

Can Kindle Read ePUB?

If you've banged around some more, you've seen some folks, including people like me, who will tell you that you can use an ePUB to Kindle formatting process. You upload an ePUB at the KDP, and the process will automatically create a MOBI file for you. This is absolutely true. ePUB is one of the accepted file formats at the KDP.

So, you can, then, effectively send an ePUB to a Kindle. In recent months, there have been strides in being able to directly email an ePUB to your Kindle (email address) and I'm told that it may soon be possible to side-load one, again, directly. Huzzah!

Even here at Booknook.biz, we don't "do" one-size-fits-all eBook-making; when we've completed an ePUB for a client, and it's approved, we take that file, make some tweaks, and use the revised content (with slightly different commands and instructions inside it) to create or build the final optimized ePUB file for Kindle. In other words, even today, when most formatters are giving “One File to Rule them All” to their customers, ignoring all the special things that Kindles have and can do, we still make two (2) files—one meant for the B&N’s, IngramSparks, Kobos, etc. of the world and one designated and formatted and coded especially for Amazon/Kindle. Whose eBook would you rather upload, when you’re betting your commercial success on it?

What’s so Special about your Kindle-optimized ePUB?

As we explained years ago in our article, Why is a MOBI Kindle File like a Cake? a MOBI file isn't a simple thing, like a Word file. It's complex. Inside a MOBI file is firstly, a whole copy of the source of the final, built MOBI file. So, if you uploaded a Word file, a complete copy of that will be inside the final MOBI stored on Amazon's servers. Then, there's an entire "KF7" MOBI--which means, a MOBI Kindle file that's optimized to be read on the older Kindle devices (like the K2 e-inks and the DXes). Amazon does this because they continue to support even the oldest of their e-reading devices.

Finally, there's an optimized "KF8" MOBI file, which is very much like an ePUB file, that is crafted to work best on the more modern readers, like the Fire, the Fire HDX, and that group. It's the KF8 MOBI files that will have embedded fonts, can float images next to paragraphs of text, display Dropcaps and that sort of thing. Amazon's tools build the files this way, so that every reader can have the book delivered to them in the best format suited for their particular e-reading device. It's excellent for you as both a reader, or an author. When a reader buys your book, they receive the copy of the book--either KF7 or KF8 format--that suits their device.

Today, in 2022, Booknook.biz makes that second ePUB file, and optimizes it just like (we used to for) the MOBI files—so that it’s showing at its absolute best, on all Amazon devices, from eInks to Fires to Scribes to you-name-it.  So that tables zoom and display, so that your images float and your fonts stick. 

What Are the KDP-Compatible File Formats?

Lastly, you should know what file formats you can, and cannot, upload at the KDP in an effort to build your book, or put your book on sale. You can read up on those supported file formats right here, in the KDP Help pages, which are extensive:  https://kdp.amazon.com/en_US/help/topic/G200634390

Instead of us listing those formats here, with a lot of description and explanation, it’s likely best if you bookmakr that page and keep up to date with what KDP does, and does not, accept.  Our shortlist is:

  • KPF (Kindle Create)
  • ePUB
  • MOBI (again, only for fixed-layout and comic book files).

Secondary list:

You may also upload, but neither we nor KDP recommend:

  • HTML (zipped or plain HTM file)
  • RTF (a generic word-processing format, typically available as a “save-as” option from almost every program out there, Word, Atlantis, Pages, you-name-it;
  • Plain TEXT (TXT) or,
  • PDF

We highly recommend that you don't try uploading a PDF—not for an eBook.  The results are almost always very, very poor. (For the reasons why, please see our article Why PDF's Really Don't Work At Kindle). If you're tecchie, you can try to create your own ePUB, from the PDF, manually, and upload that, because .ePUB format is accepted at the KDP, as discussed above.

Your best option is to upload a complete, fully-crafted and custom-built ePUB file, created for your own book. This method results in the fewest "surprises" at the KDP. We receive a lot of requests from prospective clients, who've tried to DIY, only to find out after they click the "Preview" button at the KDP that the results are nothing like what they expected.

If you receive your ePUB files from us, there won't be any surprises; you'll know without any doubt exactly what your file will look like on your reader's Kindle device.  And that's the best eBook Format for Kindle--the one that doesn't give you any unpleasant surprises. 

So, here in 2022, this is Hitch, signing off and I hope that this updated information is helpful to you.