So you’ve got a Kindle. Maybe it’s the flashy new Colorsoft with that vibrant display, or perhaps you’re rocking a battle-scarred Paperwhite from five years ago. You find a great deal on an ebook from a third-party site, but then you pause. Will this even open?
Honestly, the whole "what format books for Kindle" question used to be a total nightmare. For years, Amazon acted like a grumpy gatekeeper, forcing everyone to use their weird, proprietary files while the rest of the world used a universal standard. But things have changed—mostly for the better.
If you just want the quick answer: EPUB is now your best friend, but your Kindle technically doesn't "read" it. It's a bit of a trick. Let’s get into the weeds of how this actually works in 2026.
The Big Shift: Why Everyone is Talking About EPUB
For a long time, if you tried to put an EPUB file on a Kindle, the device would basically just stare at you blankly. You had to use clunky software like Calibre to convert it to MOBI or AZW3 first.
But Amazon finally gave in. Sorta.
Nowadays, if you use the Send to Kindle service—whether that’s via the website, the mobile app, or emailing the file—Amazon accepts EPUB files. Behind the scenes, their servers take that EPUB, chew it up, and spit out a Kindle-native file (usually AZW3 or KFX) that your device actually understands.
✨ Don't miss: IG Story No Account: How to View Instagram Stories Privately Without Logging In
It’s seamless. You send an EPUB; a book appears on your Kindle. You don't have to be a tech wizard anymore.
The "Native" Formats: AZW3 vs. KFX
When you buy a book directly from the Kindle Store, you aren't getting an EPUB. You’re getting one of Amazon's "native" children.
AZW3 (Kindle Format 8)
This was the gold standard for a long time. It replaced the old-school MOBI and allowed for much prettier books. We're talking actual fonts, better CSS support, and layouts that don't look like a 1995 GeoCities page. Most sideloaded books you transfer via a USB cable will likely be in this format.
KFX (Kindle Format 10)
This is the "fancy" one. If you notice your book has "Enhanced Typesetting" enabled, you're reading a KFX file. It handles things like ligatures (where the 'f' and 'i' in "fire" look like one elegant character) and better hyphenation. It makes the digital page look more like a real, printed book.
Basically, KFX is what makes the Kindle experience feel premium. However, you can't really "make" a KFX file easily yourself; it's mostly something Amazon generates for their own store or through their "Kindle Create" software for authors.
🔗 Read more: How Big is 70 Inches? What Most People Get Wrong Before Buying
What Happened to MOBI?
MOBI is dead. Okay, maybe not "dead" dead—if you have old MOBI files on your device, they’ll still open. But as of 2026, Amazon has officially stopped supporting MOBI for new document uploads.
Why? Because MOBI is ancient. It’s like trying to run a modern app on a flip phone. It doesn't support the high-resolution layouts or the advanced typography features that modern e-ink screens are capable of. If you have old MOBI files, it’s probably time to convert them to EPUB and re-upload them.
The Kindle Scribe Factor
If you’re using a Kindle Scribe, the format game gets even weirder. When you send a PDF to a Scribe, you have two choices. You can send it as a "standard" PDF, which lets you write directly on the page—great for marking up a contract.
Or, you can use the "Convert" option. This turns the PDF into a reflowable Kindle format. You lose the original layout, but you gain the ability to change font sizes and use "Sticky Notes" for your handwriting.
Starting in early 2026, Amazon even started allowing readers to download DRM-free versions of their purchased books in EPUB and PDF directly from the "Manage Your Content" page. This is a massive win for "ownership" advocates who were tired of being locked into the Amazon ecosystem.
💡 You might also like: Texas Internet Outage: Why Your Connection is Down and When It's Coming Back
Formatting at a Glance
Since I promised to avoid those boring, identical bullet points, let’s look at the "big three" options for your files:
- EPUB: Use this for 99% of your sideloading needs via Send to Kindle. It’s the easiest path and keeps your library synced across all your Kindle apps.
- PDF: Keep this for textbooks or documents where the layout must stay exactly the same. Be warned: on a small 6-inch Kindle screen, reading a PDF is a recipe for a headache because you'll be zooming and scrolling constantly.
- KPF (Kindle Package Format): You'll only care about this if you're an author using Kindle Create. It’s the bridge between your Word doc and the final book on the store.
The USB Secret
If you’re a privacy nut and don't want to send your files to Amazon’s servers, you can still go "old school." Plug your Kindle into your computer with a USB-C cable. It’ll show up like a thumb drive.
But remember: if you drag and drop an EPUB here, it will not work.
For the USB method, you must use AZW3 or KDF. This is where a tool like Calibre becomes essential. It lets you manage your library locally and converts the files before they ever touch your device.
Actionable Steps: How to Get the Best Results
Stop stressing about the "perfect" format and just follow this workflow:
- Check for DRM: If you bought a book from another store (like Kobo or Google Play), it might have Digital Rights Management. You'll need to remove that first (if legal in your jurisdiction) before it will work on a Kindle.
- Use the Web Uploader: Honestly, just go to
amazon.com/sendtokindle. It's the most reliable way to get an EPUB onto your device. You can drag and drop files up to 200MB now. - Subject Line "Convert": If you are emailing a PDF and you want it to act like a real ebook (where you can change the text size), put the word "convert" in the subject line of your email. Amazon’s AI will handle the rest.
- Verify the Cover: Sometimes sideloaded books don't show the cover image. If you use the Send to Kindle service, this usually fixes itself once the book syncs. If you use USB, you might need to use Calibre to "fix" the metadata.
Kindle's relationship with file formats is finally maturing. We’re moving away from the "walled garden" and toward a world where your books go where you go. Just stick to EPUB for your uploads and let Amazon's servers do the heavy lifting.
Check your "Personal Document Settings" in your Amazon account to make sure your approved email list is up to date. Once that's set, you can fire over books from any device in seconds.