Important Notice: as of midsummer, 2021, this article is outdated. Please refer to our updated article for the latest, greatest, and accurate information. Again, this article contains outdated and not-useful information; refer only for historical purposes.
About eBook Formats
One of the questions that we are often asked 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? Really, there are only two eBook formats that are still remaining in the USA, and, when you look around, in the world. Those formats are:
- ePUB: which stands for ePUBlication (clever, eh?), which is used by B&N, iBooks, Sony, KoboBooks, and Google, and,
- MOBI format, which 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 on Kindle, to the idea that using Word is the best "Kindle eBook format." The bottom line is, the files that Amazon sells to its readers are, by and large, a single file format, called "MOBI."
What Format Does Kindle Use?
Now, if you've run across various forums, you may have seen people refer to AZW format, or AZW3 format. The former 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.
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 ePUB Kindle. But before you do that, you need to understand the ePUB format--which isn't something that most DIYers want to do. 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 MOBI file for Kindle. And we do that using KindleGen, an Amazon tool, rather than doing any conversion at the KDP itself.
What's Inside a MOBI file?
As we mentioned in our recent 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 great 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.
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. If you're doing it yourself, the KDP will take files uploaded in .DOC and .DOCX format (Word or Word equivalents), .TXT files, HTML files (guidelines apply!), and PDF's and try to convert those for you. We highly recommend that you don't try uploading a PDF--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 tecchy, you can try to create your own ePUB 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 MOBI file, created for your own book. This method results in the fewest "suprises" 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 create or have created a MOBI file, 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 unpleansant surprises.