EPUB vs MOBI: Which E-book Format Should You Use?
MOBI is deprecated. EPUB is the future. Here's a complete breakdown of both formats and what it means for your Kindle reading.
The Short Answer
Use EPUB. Amazon deprecated MOBI in 2022. The Send to Kindle service now accepts EPUB directly, and MOBI files can no longer be sent via email to Kindle devices. Unless you have a very old Kindle that hasn't been updated, there is no reason to use MOBI in 2026.
What is EPUB?
EPUB (Electronic Publication) is an open standard for digital books, maintained by the W3C. It uses web technologies (HTML, CSS, XML) to create reflowable content that adapts to any screen size. EPUB is supported by virtually every e-reading platform: Apple Books, Google Play Books, Kobo, Nook, and now Kindle.
The current version, EPUB 3.3, supports rich typography, embedded multimedia, accessibility features, and both reflowable and fixed-layout content.
What is MOBI?
MOBI (Mobipocket) is a proprietary e-book format originally created by Mobipocket SA, which Amazon acquired in 2005. It was Kindle's primary format for personal documents for over a decade. MOBI is based on the Open eBook standard but with Amazon-specific extensions.
MOBI has significant limitations compared to EPUB: no support for modern CSS, limited typography options, larger file sizes, and no multimedia support. Amazon replaced MOBI internally with AZW3 (KF8) and later KFX, while keeping MOBI as a legacy delivery format.
Detailed Comparison
| Feature | EPUB | MOBI |
|---|---|---|
| Standard | Open (W3C) | Proprietary (Amazon) |
| Current Status | Actively maintained | Deprecated (2022) |
| Kindle Email Delivery | Supported | No longer accepted |
| Send to Kindle App | Supported | Limited support |
| Typography | Full CSS3 support | Basic styling only |
| Audio/Video | Supported (EPUB 3) | Not supported |
| File Size | Smaller (ZIP compression) | Larger |
| Fixed Layout | Supported | Not supported |
| Accessibility | Full ARIA support | Minimal |
| Other E-readers | Universal support | Kindle only |
| Maximum File Size | No inherent limit | ~650 MB theoretical |
Why Did Amazon Deprecate MOBI?
Amazon had been gradually moving away from MOBI for years. The format was too limited to support modern e-book features like enhanced typography, responsive layouts, and embedded multimedia. Internally, Amazon had already replaced MOBI with AZW3 (KF8) and KFX for Kindle Store deliveries.
By accepting EPUB via Send to Kindle and dropping MOBI email support, Amazon effectively acknowledged that EPUB is the superior format for e-book content. This was a welcome change for readers and publishers who no longer needed to maintain separate MOBI versions of their books.
What About AZW3 and KFX?
AZW3 (also called KF8) is Amazon's enhanced format, conceptually similar to EPUB 3 but proprietary. When you buy a book from the Kindle Store, it's typically delivered in AZW3 or KFX format.
KFX is Amazon's latest format, offering the best typography and layout features on Kindle devices. It's exclusively used for Kindle Store purchases and cannot be created by third-party tools.
For personal documents and sideloaded books, EPUB is the way to go. Amazon converts your EPUB internally when you send it to your Kindle, ensuring optimal rendering on your specific device.
What Should You Do With Your MOBI Files?
If you have a collection of MOBI files, you have a few options:
- Convert to EPUB using Calibre (free, open-source e-book management tool)
- Transfer via USB — MOBI files still work when copied directly to a Kindle via USB
- Keep them as-is — If they're already on your Kindle, they'll continue to work
For new books, always choose EPUB when available. It's the more capable format and the one Amazon will continue to support going forward.
The Bottom Line
EPUB has won. It's the open standard supported by every major platform, it offers better features than MOBI, and even Amazon — the last holdout — now accepts it. If you're still converting EPUB to MOBI out of habit, you can stop. Just send your EPUB files directly to your Kindle.
For the best experience, prepare your EPUB files with clean metadata before sending to Kindle. It takes seconds and ensures your books look great in your library.
Ready to send EPUBs to your Kindle? Use our free converter to validate and optimize your EPUB files, then follow our Send to Kindle guide.