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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. 

Transcript of the Video (for those who'd rather read!):

Do I need an ISBN to Sell my Indy-Pubbed Book?

For eBooks, the answer is nearly an unequivocal NO.  If you're going to be selling your eBook at Amazon, B&N, iBooks or KoboBooks, it's a definite no.  Given that that's the list of most self-publishing retail portals, that's pretty much the answer:  NO.  

But:  if you're publishing through an aggregator or distributor, like Smashwords or Draft2Digital, the answer is maybe--you need to ask them.  

If you are putting your book out in Print, yes, you will need an ISBN. You can acquire an ISBN, in the USA, by going to RR BOWKER. If you need more than 1 ISBN, the 10-pack, at $250, is your best bargain (10 ISBN's for $250, versus 1 ISBN for $125.00). Easy math, right? If you have print and digital, NO, you cannot reuse your print ISBN for your eBook. If you have a formerly-published print book, NO, you cannot reuse the ISBN for a new edition of the book, a new version of the book, or an eBook version of the book. If in doubt, read your retailer's FAQs.

For a more detailed explanation about ISBNs, please read our in-depth article, Do You Need an ISBN for Self-Publishing? All the ISBN news that's fit to print!

This has been Hitch from Booknook.biz, thanks for watching!

What Do I Do If I Have InDesign Files?

Well, the best alternative is to have us take a look at them, to see if we can give you the benefits of Conversion from InDesign.  However, for some folks, that's not a possibility--their print layout people won't give them the source files, for whatever reason. They'll only output a PDF.  If that's the case, keep reading:  

Conversion to ebook from any word-processing format is less expensive, by far, than converting from PDF.  If your PDF was made with InDesign, visit the following link for exporting RTF (Rich Text Format, a word-processing format that is compatible with every type of word-processor in existence) from the final print file (PDF):  http://adobe.ly/Ujw1wn .

This is NOT the same as "Save as....RTF" in InDesign or Adobe Acrobat. This process, at the link, gives you a much better output to be used for eBook conversion and formatting.

Use the instructions in the first section "Export Text."  You can even use the Indesign Tagged Text option, which will retain all formatting.  The regular export option will retain all normal formatting, like bold, italics, etc.

Sending us, or any conversion house, a word-processing file (Word, Open Office, Libre Office, Word Perfect, Scrivener, etc.) will save you a lot of money.

If you have a PDF, but either don't have the InDesign Files, there isn't a good way to turn it into a word-processed file, that's usable by the normal, non-geeky person.  Those online "convert your PDF to Word!" websites do not work. While what comes out from those online sites looks okay, it's a mess "underneath," in the code, which is what we use to make your book. 

If you do have the InDesign files, or your designer does, use the information at that link to obtain a good source file for your conversion.  Make sure, however, before your InDesigner sends them, that s/he concatenates them, so that the file we get is a single file, in the right order.   This is important; if we have to take the time to sort the files out and concatenate them in the correct order, we'll have to charge for the clerical time required to do this work. 

But seriously:  if you have access to your InDesign files, the BEST alternative is to have us make the book from those files.  It's a lot less expensive than conversion from PDF, and you get an eBook product that looks a lot like your print book.


If you are an AOL user, you might have trouble downloading or saving attachments from browsers or from within your email, because of the way AOL has its email set up.  Please read these instructions from AOL/AIM, (scroll down the page for "downloading") to learn how to save a file from your email to your computer without opening it first.  Go HERE to read the instructions: How To Download Attachments from AOL

What Does "Metadata" mean?

Metadata--literally, meaning "data about data"--(you can't make this stuff up!) is used by search engines, libraries, bookstores, etc., to help people categorize and locate books.  Metadata "tags" are like individual keywords--like the things you see on Amazon in the tag list--words that people might use in searching for your book, or a book like yours.  The Metadata "description" is a paragraph--think of  it like the blurb on the back of your book.  What will hook people into reading it?

There's a great article on PBS.org, from 2010, that explains metadata in minute detail, and it's well worth reading; you can find it here:  http://www.pbs.org/mediashift/2010/10/a-self-publishers-guide-to-metadata-for-books285.html .  I highly recommend reading it, in order that you can understand, and take advantage of, the metadata fields (keywords and description) available to you, not only at Amazon, Nook, etc., but as part of the information that we embed, invisibly, inside your ebook, helping search engines and retailer searches find your novel, biography, poems or other book.

Need help figuring out what keywords to use?  Search Amazon for books in your niche or genre that are at the top of the charts, and see what keywords (tags) they are using; compile a list, and then pick the ten best.  Don't reinvent the wheel! 

Do You Need Some Novel-Writing Essentials?

Are you a new writer, just starting out?  Or an experienced writer, looking to polish your craft, preparatory to publishing?  Here at Booknook.biz, we only recommend the places, courses, people and resources that we've used, tried, and in which we believe. Do you need a critique group, but want to stay away from the harsher free-for-alls available on the Net?  Then the Holly Lisle courses may be for you.  Are you trying to world-build, with epic fantasy?  Again, the Lisle courses have something you can use, all the way down to building your own language.  

Check out The Writer's Boot Camp!

The Writer's Boot Camp forums are divided by courses and each class within that course, and hundreds of students may be taking the same class as you are, at the same time.  The forums are fully moderated, and the action is never "too" rough and tumble for even the faintest of heart to deal with.  I know that I hear, around the Net, quite a bit, that people are afraid to use critique groups because "they're too mean," and that is never an issue at the WBC forums.  

The mini-clinics and bigger courses are both excellent.  If you're hesitant about trying the bigger courses, try one of the Mini-clinics first (they're incredibly affordable and helpful; I'm a big fan of the Plot Clinc myself) and get your feet wet before you jump in to deeper waters.

There's something here for literally every writer, at every stage of his or her career:  


How to Write Page-Turning Scenes

How to Write Dialogue with Subtext

Professional Plot Outline Mini Course

Create a Plot Clinic

Create a Character Clinic

Free Flash Fiction Class


21 Ways to Get Yourself Writing When Your Life Has Just Exploded

How to Find Your Writing Discipline

How to Motivate Yourself Workshop

How to Beat Writer's Block

Mugging the Muse (hint: this one is FUN!)


7-Day Crash Revision Workshop

How to Revise Your Novel

WORLD-BUILDING: A don't-miss for fantasy writers!

Create a Culture Clinic

Create a Language Clinic

Create A World Clinic


How to Think Sideways

How to Write a Series

Writing Clinics Bundle


Some of these courses are simply a BLAST.  I know that people have told me that Mugging the Muse is a hoot, and I enjoyed the Page-Turning Scenes mini-course.  I hope you'll find something here that you can use to help you achieve your writing goals.  

Or, if you don't see anything here just yet, take a browse at the How To Think Sideways Store:


As Holly Lisle says:  write with joy!  And good luck to you from the folks at Booknook.biz.  We hope you find our Resources helpful.

Meowy Christmas!

Christmas 2024!

Yup, it's Christmas 2024!

See you again on January 3rd! Admin is closed until then!

Seriously--we "mostly" close from December 24th-ish until the middle of the week, first week of January. Production is still steaming along, but admin takes a desperately-needed break for ~10 days. We'll answer any emails that seem in dire straights, but generally speaking, we're mostly gone for that period of time.  See ya when we return!--Merry Christmas and a Happy New Year!