iloveepub2026-09-12 · 6 min read
What Format Does Kindle Support? A Complete Guide
Kindle reads AZW, AZW3, KFX, MOBI, PDF and EPUB via Send to Kindle. Every format supported, how each behaves on a small screen, and how to get files there.
KindleEPUBFormats
Kindles are the best-selling e-readers on the planet, and also the pickiest about file formats. Where a Kobo or PocketBook happily opens an EPUB you downloaded from anywhere, a Kindle has its own family of formats — and for years it pointedly refused to touch EPUB at all.
That changed in 2022, but not in the way most people assume. Kindles still don't open EPUB files directly. Here is exactly what they do support, what each format is good for, and how to get your own files onto a Kindle without losing your mind.
The short answer
Formats Kindle devices open natively (via USB or storage): AZW, AZW3, KFX, MOBI, TXT, PDF, and image files.
Formats accepted through Send to Kindle (converted automatically in the cloud): EPUB, DOC, DOCX, HTML, TXT, RTF, and PDF — with EPUB being the one Amazon now recommends.
The one combination that fails: copying an EPUB onto a Kindle over USB. The device ignores it. The file has to go through Send to Kindle, which converts it into Amazon's own format before it reaches the device.
Formats Kindle devices read natively
| Format | What it is | Native USB | Via Send to Kindle |
|---|---|---|---|
| AZW | Original Kindle format (DRM-era MOBI variant) | Yes | — |
| AZW3 (KF8) | Modern Kindle format, rich styling | Yes | — |
| KFX | Newest Kindle engine, enhanced typesetting | Yes | — |
| MOBI | Old industry format | Yes | No — retired in 2022 |
| TXT | Plain text | Yes | Yes |
| Fixed pages | Yes | Yes | |
| EPUB | Open reflowable standard | No | Yes — converted |
| DOC/DOCX/RTF/HTML | Documents and web pages | No | Yes — converted |
AZW and AZW3
AZW is the original Kindle format, essentially MOBI with Amazon's DRM wrapped around it for books bought from the Kindle Store. AZW3 — internally called KF8 — replaced it in 2011 and is what most Kindle Store books have used since: it supports real fonts, embedded styling, drop caps, and HTML5/CSS layout.
If you buy a book from Amazon today, you receive it in one of these Kindle formats, usually wrapped in DRM tied to your device. You never see or manage the format — it simply arrives.
KFX
KFX is the newest layer, introduced alongside Amazon's enhanced typesetting engine around 2015. Books delivered as KFX get better hyphenation, improved kerning, and page-layout niceties that approach print. You can't choose to produce a KFX yourself in any practical way — Amazon's pipeline creates it — and Send to Kindle deliveries to recent devices often end up as KFX automatically.
MOBI: the format Amazon retired
MOBI is the grand old format of the ebook world, descended from the Palm Pilot era. Every Kindle ever made can still read a MOBI you load over USB — but since August 2022, Send to Kindle no longer accepts MOBI files, and the Kindle Store stopped using it for new reflowable books long before that.
Amazon's own explanation was blunt: MOBI doesn't support the newest Kindle typography features, and EPUB does a better job as an incoming format. So MOBI today is a legacy option — fine if you have an archive of old MOBI books, wrong as a target format for anything new.
How EPUB works on Kindle: Send to Kindle
Here is the nuance most "Kindle doesn't support EPUB" articles get wrong. Since mid-2022, EPUB is Amazon's recommended format for personal documents. You email or upload an EPUB, Amazon's conversion turns it into AZW3 or KFX in the cloud, and it lands on your device as a proper Kindle book — with sync, notes, and dictionary support.
The practical routes:
- The Send to Kindle web page and app — drag in an EPUB (or DOC, PDF, and friends), pick your devices, done. Files up to 200 MB.
- Email — every Kindle account has an @kindle.com address; attach the EPUB and send. The cap is 50 MB per email.
- From your phone — the share sheet's "Send to Kindle" option accepts EPUB attachments directly.
One honest caveat: the conversion happens on Amazon's servers. If keeping a file strictly on your own devices matters to you, do the local processing before sending — for example, compress a bloated EPUB in your browser first, so what leaves your hands is the smallest possible file. And of course, DRMed EPUBs from other stores won't convert; the DRM must be dealt with by whoever sold the book, not by conversion tools.
PDF on Kindle: possible, rarely pleasant
Kindles open PDFs natively — no conversion involved. The experience is exactly what you'd expect from putting a fixed letter-sized page on a six-inch screen: readable if the PDF has generous type, miserable if it's a two-column academic paper.
You can ask Send to Kindle to convert a PDF into reflowable Kindle format, but treat that as a coin flip: it works nicely on simple, text-heavy PDFs and garbles anything with complex layout. A scanned PDF — pure page images — has no text to extract and will never convert well. (The general rule is the same one our PDF to EPUB guide follows: text-layer PDFs convert, scans don't.)
If you must read a PDF on a Kindle, prefer the larger screens — a Kindle Scribe or an 10-inch model turns "squinting" into merely "small."
EPUB vs MOBI vs PDF for your Kindle
If you're assembling your own library, the decision is short:
- Incoming format for Send to Kindle: EPUB. Best typography support, actively recommended by Amazon, handles images and tables well.
- Old MOBI files you already own: keep loading them over USB; they still work.
- Print-fidelity documents (forms, papers): PDF, opened natively, on the biggest screen you have.
And if your starting point is a PDF you'd rather read comfortably, the two-step path is: convert the PDF to EPUB (on a text-based PDF this works well), then send the EPUB to your Kindle. You get reflowable text instead of a panning simulator.
What about other e-readers?
Everything above is Kindle-specific. The wider e-reader world standardized on EPUB decades ago:
- Kobo, PocketBook, Onyx Boox, and most non-Amazon readers open EPUB natively — drag it onto the device and read.
- Apple Books and Google Play Books both import EPUB directly.
- Desktop: Calibre on Windows/Mac/Linux manages and converts between all of these formats locally.
This is why EPUB remains the sensible master format for a personal library: every ecosystem either reads it directly or, in Amazon's case, converts it on arrival. For a deeper comparison of the two dominant formats themselves, see EPUB vs PDF: which should you use? — and if you just want to check what's inside an EPUB without installing anything, you can open it in your browser with the reader we're building.
The bottom line
A Kindle's native languages are AZW, AZW3, KFX, and MOBI — but the format you should feed it in 2026 is EPUB, through Send to Kindle, which converts it automatically. MOBI is retired as an incoming format, PDFs open but only truly work on big screens, and a plain EPUB copied over USB is the one thing a Kindle will silently ignore.
Keep your library in EPUB, convert only at the last step, and — whatever tool you use to shrink, merge, or split your books first — favor the ones that run locally in your browser, so your files only ever travel where you send them.