Ebook Formats Explained: EPUB, MOBI, AZW3, and PDF Compared
The ebook market uses several formats that aren't always compatible with each other. Buying a book on Amazon and wanting to read it on a Kobo can cause headaches. This guide clarifies the landscape.
The four main formats
EPUB — the open standard
EPUB (Electronic Publication) is the standard format defined by the W3C and IDPF. It uses reflowable text: content automatically adapts to screen size and the reader's chosen font size.
- Supported by: Kobo, Apple Books, Google Play Books, Adobe Digital Editions, most readers except Kindle (without conversion)
- Versions: EPUB 2 (basic), EPUB 3 (multimedia, JavaScript, MathML support)
- Best for: fiction, non-fiction, textbooks — any book where reflowable text works well
MOBI — the legacy Kindle format
MOBI was Kindle's native format until 2022. Amazon deprecated it in favor of KFX and AZW3, though older Kindles still read it.
- Supported by: all Kindle devices, Kindle app
- Limitations: doesn't support modern EPUB 3 features; inferior typographic quality compared to AZW3
- Status: deprecated — Amazon no longer accepts MOBI for new publications
AZW3 / KFX — the modern Kindle format
AZW3 (also called KF8) is MOBI's successor. It supports CSS3, custom fonts, and EPUB 3 features.
KFX is the most recent version, with improved typography handling and support for Kindle Enhanced Typesetting.
- Supported by: all modern Kindle devices, Kindle app
- Not compatible with: non-Amazon devices and apps
- Best for: Amazon KDP exclusive publishing
PDF — the fixed format
PDF is not a reflowable ebook format — it's a fixed-page representation. Text doesn't adapt to screen size.
- Supported by: everything (every device and app can read PDFs)
- Downside: on small screens requires zooming and horizontal scrolling
- Best for: technical books with complex layouts (tables, code, charts), documents that must preserve exact layout
Device compatibility
| Device / App | EPUB | MOBI | AZW3 | |
|---|---|---|---|---|
| Kindle Paperwhite | ❌* | ✅ | ✅ | ✅ |
| Kobo Clara | ✅ | ✅** | ❌ | ✅ |
| Apple Books (iOS/macOS) | ✅ | ❌ | ❌ | ✅ |
| Google Play Books | ✅ | ❌ | ❌ | ✅ |
| Kindle App (mobile) | ❌* | ✅ | ✅ | ✅ |
*Kindle accepts EPUB by emailing it to your @kindle.com address — Amazon converts it automatically. **Kobo can read MOBI with format limitations.
How to convert between ebook formats
With Calibre (free, recommended)
Calibre is the most complete ebook manager. It converts between all formats:
- Download Calibre (free, open source)
- Add the book to your library
- Right-click → Convert books → Convert individually
- Select the output format
- Click OK
Online
- Go to KaijuConverter — EPUB to PDF or whichever pair you need
- Upload your ebook file
- Download in the target format
Which format to publish on each platform
| Platform | Format to deliver |
|---|---|
| Amazon KDP | EPUB 3 (Amazon converts to AZW3 internally) |
| Kobo Writing Life | EPUB |
| Apple Books | EPUB |
| Google Play Books | EPUB |
| Gumroad / direct sales | EPUB + PDF (both, for maximum coverage) |
| Draft2Digital | EPUB (distributes to all platforms) |
DRM: the locked ebook problem
Many commercial ebooks have DRM (Digital Rights Management) that prevents reading them outside the vendor's ecosystem. A Kindle book with DRM can't be read directly on a Kobo.
Calibre has plugins (DeDRM) that let you remove DRM from legally purchased books for personal use. Legality varies by country; in many European countries it's permitted for private use.
Essential ebook metadata
For publishing on any platform, your EPUB should include:
- Title and author: required
- ISBN: for broad distribution
- Cover: JPG at least 1600×2400 px (2:3 ratio)
- Description: back cover blurb
- Category and keywords: for platform discovery algorithms
- Language: declared in the OPF file
With the right format and complete metadata, your ebook reaches readers correctly on all platforms and devices.
Related conversions
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