EPUB vs. Kindle Format (AZW3/KFX) — What's the Difference and Which Should You Use?

EPUB is the international open standard for ebooks, used by Apple Books, Kobo, PocketBook, BOOX, reMarkable, and virtually every non-Amazon e-reader. Kindle uses its own proprietary formats (AZW3 and KFX). Here's how they compare and when to use each.

Quick format comparison

Attribute	EPUB	Kindle (AZW3/KFX)
Standard	Open standard (W3C/IDPF)	Proprietary (Amazon)
Works on	Any non-Amazon e-reader, Apple Books, browser extensions	Kindle devices and Kindle app only
Kindle support	Yes — natively since 2022 or via Send to Kindle conversion	Native on all Kindles
Kobo support	Native	No
Apple Books support	Native	No
DRM possible	Yes (Adobe DRM) or DRM-free	Yes (Amazon DRM) or DRM-free
Typography quality	Good — depends on reader app	Excellent on Kindle (KFX engine)
File creation	Many tools (Sigil, Pandoc, InDesign, Calibre)	Amazon KDP or conversion from EPUB
Based on	HTML5 + CSS3 in a ZIP container	HTML5 + CSS in Amazon's container (AZW3); binary KFX
MathML support	Full (EPUB 3)	Partial
Introduced	2007 (EPUB 2), 2011 (EPUB 3)	AZW3 2011, KFX around 2015

Which format should you use?

Use EPUB if: You want to read on multiple devices, you use Kobo, Apple Books, PocketBook, or BOOX, or you're converting a PDF to read on any e-reader. EPUB is the universal choice.

Use Kindle format if: You're publishing on Amazon KDP and want the best Kindle reading experience. As a reader, you don't need to think about Kindle format — Amazon handles conversion from EPUB automatically.

Converting PDF to read on Kindle

The best workflow is:

Convert your PDF to EPUB at pdf2epub.toolkit.bot
Email the EPUB to your Kindle address (or use Send to Kindle app)
Amazon converts the EPUB to Kindle format automatically during delivery
Read with full Kindle features: adjustable font, Word Wise, Vocabulary Builder

The history: MOBI → AZW → AZW3 → KFX

Amazon has used several formats over the years. MOBI (used by the original Kindle) was based on the PalmDOC format. AZW was essentially encrypted MOBI. AZW3 (KF8) added HTML5/CSS3 support. KFX is Amazon's current format with advanced typography. For readers, none of this matters — Send to Kindle handles conversion from EPUB to whatever the current Kindle format is.

What is AZW3, exactly?

AZW3 — also called KF8 or Kindle Format 8 — arrived in 2011 as Amazon's replacement for MOBI. Under the hood it is EPUB-like: HTML5 and CSS wrapped in Amazon's own container, with Amazon DRM and Kindle-specific extensions. Until 2022 it was the file you got from the Kindle Store and the file Calibre produced when you converted an EPUB for a Kindle. KFX later took over as the delivery format on newer devices.

Do you still need AZW3?

For almost everyone, no. Send to Kindle accepts EPUB and produces the Kindle-side format for you; you never create AZW3 yourself. You will still meet it in three places:

Old Kindle purchases — books bought before 2022 may download as AZW3 when you use "Download & transfer via USB". They work on Kindle but not on other readers without conversion.
A long-running Calibre library — years of past conversions leave AZW3 files behind; Calibre's viewer reads them fine.
Legacy Kindle firmware — very old devices that stopped receiving updates never gained EPUB support. For those, Calibre's ebook-convert book.epub book.azw3 and a USB copy to the documents folder is still the route.

Converting AZW3 to EPUB

DRM-free AZW3 files convert cleanly with Calibre — ebook-convert file.azw3 output.epub — and then open on Kobo, Apple Books or any other reader. DRM-protected AZW3 (most Kindle Store purchases) cannot be converted without removing the DRM first, which may not be legal where you live.

Frequently asked questions

Can Kindle read EPUB files?

Modern Kindle devices and apps can read EPUB files natively — Amazon added direct EPUB support in 2022. Older Kindle firmware requires sending the EPUB via email or the Send to Kindle app, which auto-converts it to Kindle format (AZW3/KFX) during delivery. The converted document is indistinguishable from a natively purchased Kindle book in terms of reading features.

What is the difference between AZW3 and KFX?

AZW3 (also called KF8) is Amazon's ebook format based on HTML/CSS, introduced around 2011. KFX is Amazon's newer format introduced around 2015, which adds better typography (hyphenation, justification, kerning) and Amazon-specific features like PageFlip. Both are proprietary Kindle formats. EPUBs sent to Kindle are converted to KFX on newer devices. You don't need to choose between them — Amazon handles the conversion automatically.

Is EPUB better than Kindle format?

EPUB is better for device independence: it works on Kobo, Apple Books, PocketBook, BOOX, reMarkable, and any non-Amazon reader. Kindle format only works on Amazon devices and apps. In terms of reading features, modern Kindle format (KFX) supports slightly better typography on Kindle devices. For reading specifically on Kindle, the formats are functionally equivalent once an EPUB is converted.

Can I convert EPUB to Kindle format myself?

Yes. The simplest way is to email the EPUB to your Kindle address — Amazon converts it automatically. Alternatively, use the Send to Kindle app (Windows, Mac, iOS, Android) which does the same conversion. The open-source tool Calibre can also convert EPUB to MOBI/AZW3 locally if you want a file you can transfer without Amazon's servers.

Can I convert AZW3 to EPUB?

Yes, if the file has no DRM: Calibre converts it (right-click → Convert books → Output: EPUB, or ebook-convert on the command line). Books bought from the Kindle Store carry Amazon DRM and cannot be converted without stripping it, which may not be legal in your jurisdiction. Old sideloaded conversions and DRM-free purchases convert without trouble.

What about MOBI format?

MOBI was Amazon's older Kindle format before AZW3. Amazon officially deprecated MOBI for Send to Kindle in 2022 — the app no longer accepts MOBI files. Use EPUB instead: it's the current standard, Amazon converts it properly, and it works on all other e-reader platforms too.