Guide

AZW3 (KF8) Format: Amazon's Modern Kindle eBook Format Guide

PC By Pablo Cirre • Updated May 7, 2026

AZW3 (also known as KF8 or Kindle Format 8) is Amazon's modern ebook format, replacing the aging MOBI standard in 2011. It brought Kindle's ebook capabilities in line with EPUB 3, supporting modern HTML5, CSS3, embedded fonts, and complex layouts. Understanding AZW3 is essential for anyone publishing to Kindle or managing a modern Kindle library.

What Is AZW3?

AZW3 was introduced alongside the Kindle Fire tablet in 2011 to address the fundamental limitations of the older MOBI/AZW format. While MOBI used a simplified HTML subset with no stylesheet support, AZW3 is built on:

HTML5 for content markup
CSS3 for typography and layout
OpenType/TrueType embedded fonts (subset embedding like EPUB)
SVG for scalable graphics
Fixed-layout support (essential for children's books, comics, textbooks)
Media overlays (audio synchronization for read-aloud books)

Structurally, AZW3 uses Amazon's proprietary container format wrapping the same technology stack as EPUB 3. This is why Calibre can convert between AZW3 and EPUB with high fidelity — they're built on the same HTML/CSS foundations.

AZW3 vs MOBI vs EPUB

Feature	AZW3	MOBI	EPUB 3
CSS support	✅ Full CSS3	❌ None	✅ Full CSS3
Embedded fonts	✅ Yes	❌ No	✅ Yes
Fixed layout	✅ Yes	❌ No	✅ Yes
HTML5	✅ Yes	❌ Subset only	✅ Yes
DRM	Optional (Amazon DRM)	Optional	Optional
Open standard	❌ Proprietary	❌ Proprietary	✅ W3C standard
Kindle support	✅ Full	✅ Legacy	Via Kindle app only
Non-Kindle readers	❌ Limited	❌ Limited	✅ Universal

Where AZW3 Is Used

AZW3 is the delivery format for all modern Kindle Store purchases:

Enhanced ebooks with custom fonts and complex layouts
Children's books with fixed-layout pages
Comics and manga (Kindle Comixology integration)
Textbooks with complex tables, math equations, and multi-column layouts
Kindle Unlimited content

When you buy a Kindle book today, you're almost certainly getting AZW3 (or KFX for premium content) rather than the legacy MOBI format.

Converting AZW3 Files

AZW3 to EPUB (for Kobo, Apple Books, Google Play Books):

ebook-convert book.azw3 book.epub

Calibre produces excellent EPUB output from AZW3 since both share the HTML5/CSS3 foundation. The conversion preserves fonts, styles, and layout.

AZW3 to PDF:

ebook-convert book.azw3 book.pdf

For reflowable books, Calibre produces a good PDF. For fixed-layout AZW3 (comics, children's books), PDF conversion is more reliable because page dimensions are already defined.

AZW3 to MOBI (backward compatibility):

ebook-convert book.azw3 book.mobi

This downgrades the format — you'll lose CSS styling, embedded fonts, and any fixed-layout features. Only do this if targeting very old Kindle devices.

EPUB to AZW3 (for self-publishers):

ebook-convert book.epub book.azw3

Amazon's Kindle Previewer tool also converts EPUB to AZW3 and shows exactly how the book will look on Kindle devices.

DRM on AZW3

Amazon-purchased AZW3 files have DRM applied. The technical DRM format is called "Topaz" for older files and "KFX" for premium content. DRM-free AZW3 files (from Smashwords, Draft2Digital, direct author sales) convert without restrictions using Calibre.

Creating AZW3 Files (Self-Publishers)

If you're a Kindle Direct Publishing (KDP) author:

Write in EPUB: create your book in EPUB format using tools like Vellum (Mac), Sigil, or Reedsy
Upload EPUB to KDP: Amazon converts to AZW3 automatically
Use Kindle Previewer: download Amazon's Kindle Previewer desktop tool to see exactly how your book renders across Kindle generations before publishing
Fixed-layout guide: for children's books or comics, use KDP's Fixed Layout guide with specific CSS viewport declarations

Kindle Format Roadmap

AZW3 remains the primary format, but Amazon continues developing:

KFX: used for enhanced Kindle books with features beyond AZW3 (Whispersync for Voice, print replica)
Print Replica: PDF-in-Kindle-wrapper for textbooks
Kindle Vella: serialized fiction platform using a web-first format

For most ebook publishing and conversion needs, AZW3 ↔ EPUB conversion via Calibre covers everything.

Related conversions

Frequent conversions across the catalogue:

Related conversions

Put what you just learned into practice — convert your files now in seconds, free and without registration.

Convert →

Convert →

Convert →

Convert →

Convert →

Convert →

Frequently Asked Questions

AZW is Amazon's original Kindle format from 2007 — essentially MOBI with DRM. AZW3 (also called KF8 or Kindle Format 8) is a completely redesigned format introduced in 2011 alongside the Kindle Fire. AZW3 uses HTML5 and CSS3 instead of MOBI's primitive HTML subset, supporting embedded fonts, complex layouts, fixed-layout books, and SVG graphics. All modern Kindle Store purchases use AZW3 rather than the legacy AZW format.

AZW is Amazon's original Kindle formato de 2007 — essentially MOBI com DRM. AZW3 (also called KF8 ou Kindle formato 8) is a completely redesigned formato introduced in 2011 alongside the Kindle Fire. AZW3 uses HTML5 e CSS3 em vez de MOBI's primitive HTML subset, supporting embedded fonts, complexo layouts, fixed-layout books, e SVG graphics. All moderno Kindle Store purchases usar AZW3 em vez de the legacy AZW formato.

AZW is Amazon's original Kindle Format von 2007 — essentially MOBI mit DRM. AZW3 (also called KF8 oder Kindle Format 8) is a completely redesigned Format introduced in 2011 alongside the Kindle Fire. AZW3 uses HTML5 und CSS3 anstatt MOBI's primitive HTML subset, supporting embedded fonts, complex layouts, fixed-layout books, und SVG graphics. All modern Kindle Store purchases verwenden AZW3 rather than the legacy AZW Format.

AZW is Amazon's original Kindle formato de 2007 — essentially MOBI con DRM. AZW3 (also called KF8 o Kindle formato 8) is a completely redesigned formato introduced in 2011 alongside the Kindle Fire. AZW3 uses HTML5 y CSS3 en vez de MOBI's primitive HTML subset, supporting embedded fonts, complex layouts, fixed-layout books, y SVG graphics. All moderno Kindle Store purchases usar AZW3 rather than the legacy AZW formato.

On KaijuConverter every file is processed inside an isolated container, encrypted in transit (TLS 1.3) and at rest, and automatically deleted after 60 minutes with multi-pass overwrite. We never train on, share, or analyze user content. For maximum privacy on extremely sensitive material, prefer offline tools (ImageMagick, FFmpeg, LibreOffice) that you control end-to-end.

Use Calibre (free, all platforms): add the AZW3 file, right-click → Convert books → Convert individually → choose EPUB as output. Because AZW3 and EPUB 3 both use HTML5/CSS3, the conversion preserves fonts, styles, and layout very well. The main exception is Amazon-specific DRM: Calibre cannot convert DRM-protected Kindle Store purchases without additional tools.

Use Calibre (free, all plataformas): add the AZW3 file, right-click → converter books → converter individually → choose EPUB as output. Because AZW3 e EPUB 3 both usar HTML5/CSS3, the conversion preserves fonts, styles, e layout very well. The main exception is Amazon-specific DRM: Calibre cannot converter DRM-protected Kindle Store purchases sem additional ferramentas.

Use Calibre (free, all Plattformen): add the AZW3 file, right-click → umwandeln books → umwandeln individually → choose EPUB as output. Because AZW3 und EPUB 3 both verwenden HTML5/CSS3, the conversion preserves fonts, styles, und layout very well. The main exception is Amazon-specific DRM: Calibre cannot umwandeln DRM-protected Kindle Store purchases ohne additional Werkzeuge.

Use Calibre (free, all plataformas): add the AZW3 file, right-click → convertir books → convertir individually → choose EPUB as output. Because AZW3 y EPUB 3 both usar HTML5/CSS3, the conversion preserves fonts, styles, y layout very well. The main exception is Amazon-specific DRM: Calibre cannot convertir DRM-protected Kindle Store purchases sin additional herramientas.

For 95% of use cases, yes — server-side ImageMagick, FFmpeg and LibreOffice produce identical output to the same tools on your laptop. Desktop software wins for: extremely large files (multi-GB), batch jobs of thousands of files, scripted pipelines, or content too sensitive to upload. KaijuConverter caps at 25 MB per file on the free tier (up to 2 GB on paid plans).

Not natively. AZW3 is Amazon's proprietary format. To read AZW3 on a Kobo, convert to EPUB first using Calibre. For iPhone or iPad, the Kindle app reads AZW3 files directly — sideloaded AZW3 files can be sent to the Kindle app via email (your @kindle.com address) or transferred through the Kindle app's Send to Kindle feature.

Not natively. AZW3 is Amazon's proprietary formato. To read AZW3 em um Kobo, converter to EPUB first usando Calibre. para iPhone ou iPad, the Kindle app reads AZW3 arquivos directly — sideloaded AZW3 arquivos can be enviado para o Kindle app via email (your @kindle.com address) ou transferred através de the Kindle app's enviar to Kindle feature.

Not natively. AZW3 is Amazon's proprietary Format. To read AZW3 auf einem Kobo, umwandeln to EPUB first using Calibre. für iPhone oder iPad, the Kindle app reads AZW3 Dateien directly — sideloaded AZW3 Dateien can be sent zum Kindle app via email (your @kindle.com address) oder transferred durch the Kindle app's senden to Kindle feature.

Not natively. AZW3 is Amazon's proprietary formato. To read AZW3 en un Kobo, convertir to EPUB first using Calibre. para iPhone o iPad, the Kindle app reads AZW3 archivos directly — sideloaded AZW3 archivos can be sent al Kindle app via email (your @kindle.com address) o transferred a través de the Kindle app's enviar to Kindle feature.

Most format conversions are lossy by design — JPG, MP3, MP4, WebP all discard perceptual data to save bytes. Going through a lossy intermediate compounds the loss. To minimize visible/audible drift: convert from the original master, choose a higher quality setting, and avoid converting back and forth between lossy formats.

Upload EPUB to Kindle Direct Publishing (KDP) — Amazon converts it to AZW3 automatically. This gives you the best results because EPUB is well-structured and KDP's converter is optimized for it. Alternatively, use Amazon's Kindle Create app to build your book and export directly. Before publishing, always check your book in Kindle Previewer (free desktop app from Amazon) across all Kindle device generations to catch layout issues.

Upload EPUB to Kindle Direct Publishing (KDP) — Amazon converts it to AZW3 automatically. This gives you the best results because EPUB is well-structured e KDP's converter is optimized para it. Alternatively, usar Amazon's Kindle Create app to build your book e export directly. antes publishing, always check your book in Kindle Previewer (free desktop app de Amazon) across all Kindle device generations to catch layout issues.

Upload EPUB to Kindle Direct Publishing (KDP) — Amazon converts it to AZW3 automatically. This gives you the best results because EPUB is well-structured und KDP's converter is optimized für it. Alternatively, verwenden Amazon's Kindle Create app to build your book und export directly. vor publishing, always check your book in Kindle Previewer (free desktop app von Amazon) across all Kindle device generations to catch layout issues.

Upload EPUB to Kindle Direct Publishing (KDP) — Amazon converts it to AZW3 automatically. This gives you the best results because EPUB is well-structured y KDP's converter is optimized para it. Alternatively, usar Amazon's Kindle Create app to build your book y export directly. antes publishing, always check your book in Kindle Previewer (free desktop app de Amazon) across all Kindle device generations to catch layout issues.

Yes — KaijuConverter accepts multiple files in a single drop and returns a ZIP. For very large batches (thousands of files) consider command-line tools or our API: <code>find . -name "*.heic" -exec magick {} {.}.jpg \;</code> or similar one-liners scale to millions of files when run locally.