The Ebook Format Landscape
Ebook formats are fragmented because each major retailer created their own standard. Understanding which format works where saves you a lot of frustration.
Format Overview
EPUB — The Universal Standard
EPUB (Electronic PUBlication) is the open standard maintained by the W3C. It's the format used by every major ebook platform except Amazon Kindle.
Supported by: Kobo, Apple Books, Google Play Books, Barnes & Noble Nook, PocketBook, Adobe Digital Editions, and most reading apps.
EPUB 2 vs EPUB 3: EPUB 3 (2011) supports HTML5, CSS3, audio, video, and better accessibility. Always create new ebooks in EPUB 3.
Reflowable: text adapts to screen size and reader font preferences.
MOBI — Amazon's Legacy Format
Developed by Mobipocket (acquired by Amazon in 2005). Amazon used MOBI as the Kindle format until 2011.
Status in 2024: effectively deprecated. Amazon removed support for MOBI email delivery in 2022. Kindle devices still read MOBI files transferred via USB, but it's no longer the recommended format.
AZW3 / KF8 — Modern Kindle Format
AZW3 (also called KF8) replaced MOBI as Amazon's current Kindle format. It supports CSS3, HTML5, embedded fonts, and complex layouts.
Only works on Kindle — not compatible with any other reader.
PDF — Fixed Layout
PDF isn't really an "ebook" format — it's a document format with fixed layout. Text doesn't reflow to fit the screen, which makes it difficult to read on small e-ink displays.
Use PDF for: illustrated books, textbooks with complex layouts, comics/manga, or when you need exact pagination.
Compatibility Matrix
| Format | Kindle | Kobo | Apple Books | Google Play | Nook |
|---|---|---|---|---|---|
| EPUB | ❌ (natively) | ✅ | ✅ | ✅ | ✅ |
| MOBI | ✅ (legacy) | ❌ | ❌ | ❌ | ❌ |
| AZW3 | ✅ | ❌ | ❌ | ❌ | ❌ |
| ✅ | ✅ | ✅ | ✅ | ✅ |
For Authors and Publishers
| Platform | Submit as |
|---|---|
| Amazon KDP | EPUB or DOCX (Amazon converts to AZW) |
| Kobo Writing Life | EPUB |
| Apple Books | EPUB |
| Google Play Books | EPUB or PDF |
| Draft2Digital | EPUB or DOCX |
| IngramSpark | EPUB or PDF |
Recommendation: master your book in EPUB 3. Every major distributor accepts EPUB and converts to their format as needed. You don't need to produce MOBI or AZW3 manually.
Reading EPUB on Kindle
Amazon Kindle devices cannot read EPUB natively. Two workarounds:
-
Send to Kindle app: Amazon's app can now convert EPUB files sent from your computer or mobile (as of 2022).
-
Convert with Calibre: Calibre (free) converts EPUB to MOBI or AZW3 for sideloading via USB.
-
Convert online: EPUB to MOBI with KaijuConverter.
Reading MOBI/AZW3 on Non-Kindle Devices
If you have MOBI or AZW3 files and want to read on Kobo, Apple Books, or a phone:
- Convert to EPUB with MOBI to EPUB or AZW3 to EPUB.
- Import the EPUB into your preferred reading app.
DRM Note: Kindle books purchased from Amazon have DRM and cannot be converted. Only DRM-free ebooks (your own writing, CC-licensed content, or books without protection) can be converted.
Which Format Should You Use?
For your own ebook project:
→ Author/publish in EPUB 3
For reading on Kindle:
→ AZW3 (purchased from Amazon) or MOBI/EPUB via Send to Kindle
For reading on anything else:
→ EPUB
For printing or complex layouts:
→ PDF