October 21, 2026
MOBI vs EPUB (2026): The Definitive Author's Guide
MOBI vs EPUB in 2026: Amazon killed MOBI; EPUB wins. Learn the formats, what KDP accepts, and how to publish one clean EPUB everywhere.
TL;DR
MOBI is dead. Amazon stopped accepting MOBI uploads entirely as of March 18, 2025. EPUB is now the universal ebook format, accepted by every major retailer including Amazon KDP, Apple Books, Kobo, Google Play, and Barnes & Noble. Authors need one clean EPUB file to distribute everywhere. All those Amazon-specific formats you hear about (AZW3, KFX, KPF) are generated automatically from your upload.
If you’ve searched “mobi epub” trying to figure out which ebook format to use, the answer is simpler than it’s ever been. EPUB won. MOBI lost. The rest of this guide explains why, defines every format term you’ll encounter, and gives you a practical framework for getting your book onto every platform that matters.
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Which Format Do You Actually Need in 2026?
EPUB. That’s it.
For years, the mobi epub debate forced authors into an awkward split: create an EPUB for non-Amazon stores, then create or convert a MOBI file for Kindle. That era is over. Amazon deprecated MOBI for reflowable ebooks in June 2021 and killed it for fixed-layout ebooks on March 18, 2025. If you try to upload a MOBI file to KDP today, it will be rejected.
One master EPUB file now covers Amazon (via automatic conversion), Apple Books, Kobo, Barnes & Noble Nook, Google Play, IngramSpark, and Draft2Digital. Over 95% of independent authors publish in ebook format, and EPUB is the format that connects them to readers on every storefront.
Practitioners on Reddit’s r/selfpublish confirm this shift. The community consensus is firmly pro-EPUB, with multiple threads warning that authors who follow outdated tutorials waste hours creating MOBI files that Amazon no longer accepts.
Glossary of Ebook Formats A to Z
Every term you’ll encounter when navigating the mobi epub format world, defined in plain language.
AZW
Amazon’s original Kindle file format, built on the Mobipocket (MOBI) codebase. Legacy format. You can’t upload it, and you don’t need to create it. It exists only on very old Kindle devices.
AZW3 (Kindle Format 8 / KF8)
Amazon’s second-generation ebook format, introduced in 2011 to overcome MOBI’s limitations. AZW3 brought HTML5 and CSS3 support to Kindle, enabling embedded fonts, better layouts, and richer design. You never upload an AZW3 file. Amazon generates it internally from your EPUB or DOCX upload.
Calibre
A free, open-source ebook management and conversion tool. It runs on Windows, Mac, and Linux. Authors commonly use it to convert between formats, edit metadata, and organize ebook libraries. One Goodreads community member shared their Windows workflow: “I use Sigil for EPUB formatting and convert to MOBI format with Calibre as needed,” though the MOBI conversion step is now unnecessary.
CSS (in Ebook Context)
The stylesheet language that controls how your ebook looks, including fonts, margins, spacing, and colors. MOBI supported only partial CSS 1/2. EPUB 3 and Amazon’s newer formats support full CSS3, which is why modern ebooks look dramatically better than they did a decade ago.
DOCX
Microsoft Word’s file format. KDP, IngramSpark, and Draft2Digital all accept DOCX uploads. It works, but you sacrifice control over typography and layout compared to a properly built EPUB. For a deeper look at manuscript preparation, see our manuscript formatting glossary.
DRM (Digital Rights Management)
Copy protection applied by retailers to prevent unauthorized sharing. DRM is a retailer-level setting, not a format feature. Both EPUB and Amazon’s formats support DRM, but the implementation varies by platform. One critical requirement under the European Accessibility Act: DRM must never block assistive technology like screen readers.
Enhanced Typesetting
Amazon’s rendering system that improves font display, hyphenation, kerning, and page layouts on Kindle devices and apps. Your book qualifies for Enhanced Typesetting when you upload an EPUB or KPF file. MOBI uploads never qualified.
EPUB (Electronic Publication)
The open, vendor-independent ebook format maintained by the W3C. Technically, an EPUB file is a ZIP container holding HTML/XHTML pages, CSS stylesheets, images, and metadata. It supports reflowable text (content adapts to screen size) and is accepted by nearly every ebook retailer on the planet. When people compare mobi vs epub, EPUB wins on every technical metric and every practical one too.
EPUB 2
The older version of the EPUB standard, released in 2007. Uses HTML 4.01 and CSS 2.1. Still accepted by most platforms, but it lacks multimedia support, advanced accessibility features, and the layout flexibility of EPUB 3. If you’re creating new files, there’s no reason to target EPUB 2.
EPUB 3
The current version of the standard (version 3.3, released 2022). Built on HTML5 and CSS3. Supports embedded audio and video, JavaScript interactivity, MathML for equations, fixed-layout mode for picture books and comics, and full WCAG accessibility compliance. All major self-publishing platforms accept EPUB 3, and it is the industry default. The W3C Publishing Working Group is already planning EPUB 3.4, expected by 2027, with improvements to digital comics and fixed-layout accessibility.
Fixed-Layout EPUB
A variant where pages maintain exact positioning rather than reflowing. Used for children’s picture books, comics, cookbooks, and design-heavy titles. Amazon’s March 2025 MOBI cutoff specifically targeted fixed-layout files, since reflowable MOBI uploads had already been blocked since 2021.
If you’re working on a children’s book with fixed-layout needs, our children’s book services handle the specialist design and formatting required.
KFX (Kindle Format 10 / Kindle Format X)
The format that actually lands on a reader’s Kindle device or app when they purchase your book. KFX supports enhanced typographic features including improved hyphenation, ligatures, and drop caps. Authors don’t create KFX files. Amazon generates them automatically. For the full breakdown, see our guide on what file format Kindle uses.
Kindle Create
Amazon’s free desktop tool for formatting ebooks and producing KPF files. Available for Windows and Mac. Useful if you want to add Amazon-specific design features like themed templates, but not required. Amazon recommends it specifically for fixed-layout projects as an alternative to EPUB.
Kindle Previewer
Amazon’s free testing tool that shows exactly how your file will render across different Kindle devices and apps. Essential for catching formatting bugs before publishing. Every author uploading to KDP should run their file through this tool.
KPF (Kindle Package Format)
The output format of Kindle Create. KPF is an alternative upload format to EPUB on KDP. It’s Amazon-specific, so if you go wide (publishing on multiple platforms), KPF doesn’t help. EPUB remains the better choice for authors distributing beyond Amazon.
MOBI (Mobipocket)
Amazon’s legacy ebook format, originally developed by the French company Mobipocket SA (acquired by Amazon in 2005). MOBI files are often larger than EPUB files containing the same content. The format lacks modern CSS support, has limited font embedding, offers no accessibility features, and handles images poorly. Amazon fully deprecated MOBI for uploads as of March 2025. The mobi epub comparison is no longer a real contest.
NCX (Navigation Control for XML)
The table-of-contents file used inside EPUB 2 packages. EPUB 3 replaced NCX with an HTML-based navigation document, though many EPUB 3 files still include NCX for backward compatibility with older reading devices.
OPF (Open Packaging Format)
The metadata and manifest file inside an EPUB. It lists every file in the package, specifies reading order, and contains metadata like title, author, ISBN, and language. Your EPUB’s metadata includes your ISBN, and understanding how ISBNs work is essential for proper discoverability.
Reflowable
Text that adapts to screen size and responds to the reader’s font-size preferences. The opposite of fixed layout. Most novels, memoirs, and nonfiction books should be reflowable. This is the default behavior for EPUB and the default expectation for Kindle.
Send to Kindle
Amazon’s personal document delivery service for transferring ebooks to your Kindle. It now accepts EPUB files directly. Amazon quietly stopped accepting MOBI through Send to Kindle in 2022, another signal that the mobi epub migration was well underway before the final cutoff.
Sigil
A free, open-source EPUB editor available on Windows, Mac, and Linux. Popular with technically inclined authors who want direct control over their EPUB’s HTML and CSS. Less user-friendly than Vellum but far more flexible.
Sideloading
Manually transferring ebook files to a reading device via USB cable or email, bypassing the retailer’s store. If you sideload to a Kindle today, EPUB works. MOBI also still works on older Kindles, but there’s no practical reason to create new MOBI files for sideloading.
Vellum
A popular Mac-only formatting tool ($249.99 for ebook and print capabilities) that produces professional EPUB files and print-ready PDFs. As one author noted in a Goodreads discussion: “When you are ready to publish you simply click a button marked ‘Generate’ and Vellum automatically formats your book for all ebook platforms (including Kindle, Kobo, Apple etc) and for print books.” It’s the most common tool mentioned in author communities for a reason.
MOBI vs EPUB: The Full Comparison
Here’s the definitive side-by-side view of how these formats stack up in 2026, along with Amazon’s proprietary formats for context:
| Feature | EPUB | MOBI | AZW3/KF8 | KFX |
|---|---|---|---|---|
| Status (2026) | Active standard | Deprecated | Amazon internal | Amazon delivery |
| Open standard | Yes (W3C) | No | No | No |
| Upload to KDP | Yes | No longer accepted | Not an upload format | Auto-generated |
| Non-Amazon stores | Universal | Kindle only (legacy) | Kindle only | Kindle only |
| CSS support | CSS3 | CSS 1/2 (partial) | CSS3 | CSS3+ |
| Embedded fonts | Full | Limited | Full | Full |
| Accessibility | WCAG-ready | None | Limited | Limited |
| Fixed layout | Yes | No (since March 2025) | Yes | Yes |
| File size | Smaller | Larger | Comparable to EPUB | Comparable to EPUB |
| Multimedia | Audio, video, JS | None | None | Limited |
The MOBI Deprecation Timeline
The death of MOBI didn’t happen overnight. It was a slow, predictable phase-out:
- June 28, 2021: Amazon deprecated MOBI for reflowable Kindle ebooks.
- 2022: Send to Kindle stopped accepting MOBI files.
- March 18, 2025: Amazon ended MOBI acceptance for fixed-layout ebooks, completing the transition.
One important nuance from MobileRead forums (a dedicated ebook community): the end of MOBI uploads does not mean the format vanishes entirely. Amazon still produces MOBI-format files for delivery to very old Kindle devices that can’t handle newer formats. Existing MOBI books in reader libraries also remain functional. But for any new or updated content, authors must use EPUB, DOCX, or KPF.
What Amazon Actually Does With Your EPUB
Understanding the mobi epub shift requires knowing what happens after you hit “upload” on KDP. The process goes like this:
- You upload an EPUB (or DOCX, or KPF) to KDP.
- Amazon’s system converts your file to its internal KF8 format.
- When a reader purchases your book, Amazon delivers a KFX file optimized for their specific device or app.
- If the reader uses a very old Kindle, Amazon may deliver an AZW3 or even MOBI version for compatibility.
The key takeaway: you never choose AZW3 or KFX. You provide a clean source file, and Amazon handles the rest. EPUB produces the best conversion results because it shares the same underlying technology (HTML5, CSS3) as Amazon’s modern formats.
Testing matters. Before publishing, run your EPUB through Amazon’s free Kindle Previewer to catch rendering issues across different devices. For the full upload walkthrough, our KDP self-publishing guide covers every step.
EPUB for Wide Distribution
Amazon holds roughly 60 to 70% of U.S. ebook sales and a commanding 72% of the e-reader market. But that still leaves a meaningful chunk of readers on other platforms. If you sell wide, one EPUB file is your ticket to all of them:
- Apple Books: EPUB (required)
- Kobo: EPUB (required)
- Barnes & Noble Nook: EPUB (required)
- Google Play Books: EPUB (required)
- IngramSpark: EPUB (required for ebooks)
- Draft2Digital: EPUB (required)
No store outside Amazon ever accepted MOBI. So for wide-distribution authors, the mobi epub question was always settled. EPUB was the only choice that scaled. Now that Amazon accepts EPUB too, the case for maintaining separate format workflows has completely collapsed.
Curious about selling on multiple platforms simultaneously? Our guide on publishing on Amazon and other platforms walks through the logistics.
EPUB 3 and Accessibility: Why It Matters Now
EPUB 3 isn’t just a technical upgrade. It’s becoming a legal requirement in some markets.
The European Accessibility Act (EAA) began applying to ebooks and e-reading software sold to EU consumers on June 28, 2025. The practical compliance target is a reflowable EPUB 3 file meeting EPUB Accessibility 1.1 at WCAG Level AA.
In concrete terms, that means:
- Structured, semantic HTML markup
- Working navigation (table of contents, page list)
- Text alternatives (alt text) for all images
- A declared language in the metadata
- Accessibility metadata embedded in the file
- DRM that never blocks screen readers or assistive technology
MOBI was never capable of meeting any of these requirements. It lacked semantic markup, had no accessibility metadata support, and offered no mechanism for screen reader compatibility. This is another structural reason the format had to die.
Even if you’re a U.S.-based author, this matters. If your book is available for purchase by EU readers through any global retailer (and most distribution services make your book available globally by default), accessibility compliance applies. The 31% of U.S. adults who read ebooks in 2025 are just one segment of a global ebook market worth an estimated $14.9 to $18 billion.
Tools for Creating EPUB Files
You don’t need to write HTML by hand to produce an EPUB. Several tools handle the heavy lifting:
Vellum ($249.99, Mac only): The most popular option in author communities. Produces beautiful, retailer-ready EPUB and print files with minimal effort. The limitation is Mac exclusivity and the upfront cost.
Calibre (free, Windows/Mac/Linux): An open-source Swiss army knife for ebook management. Converts between formats, edits metadata, and organizes libraries. Not a design tool, but invaluable for format conversion and library management.
Sigil (free, Windows/Mac/Linux): A dedicated EPUB editor that gives you direct access to the HTML and CSS inside your file. Steep learning curve, maximum control.
Kindle Create (free, Windows/Mac): Amazon’s own tool, producing KPF files. Best for authors who publish exclusively on Amazon and want access to Amazon-specific design templates.
Scrivener ($49, Windows/Mac): A writing tool that compiles manuscripts to EPUB. The EPUB output is functional but often needs cleanup in Sigil or another editor.
If budgeting for tools and services feels overwhelming, our self-publishing cost breakdown puts formatting costs in context alongside editing, covers, and distribution.
Common Ebook Formatting Mistakes
Based on patterns from Reddit, Goodreads, and KDP community forums, these are the mistakes authors make most often with mobi and epub files:
Uploading MOBI to KDP. It’s 2026, and authors following outdated tutorials still try this. KDP will reject the file. If you have legacy MOBI files, convert them to EPUB using Calibre before uploading.
Following outdated guides. Many top-ranking articles and YouTube tutorials were written before Amazon’s deprecation timeline. If a guide tells you to create both MOBI and EPUB versions, it’s out of date.
Using EPUB 2 for fixed-layout books. Fixed-layout support in EPUB 2 is inconsistent. Use EPUB 3 for children’s books, comics, cookbooks, or any title with page-exact layouts.
Skipping device testing. Your EPUB might look perfect in Sigil but break on a Kindle Paperwhite or an old Kobo Clara. Always preview on actual devices or at minimum use Kindle Previewer and Adobe Digital Editions.
Forgetting alt text on images. This is both an accessibility issue and, since June 2025, a potential legal compliance issue for EU sales. Every image in your EPUB should have descriptive alt text.
Using CMYK images. EPUB and Kindle formats require RGB color space. CMYK images (which are standard for print) will render incorrectly or be rejected. Convert all images to RGB before embedding them in your EPUB.
Ignoring metadata. Your EPUB’s OPF file contains metadata that retailers use for discoverability: title, author name, description, ISBN, language, subject categories. Incomplete metadata means your book doesn’t show up where it should.
What to Upload Where: A Quick Reference
| Platform | Accepted Ebook Formats | Best Choice |
|---|---|---|
| Amazon KDP | EPUB, DOCX, KPF | EPUB |
| Apple Books | EPUB | EPUB |
| Kobo Writing Life | EPUB | EPUB |
| Barnes & Noble Press | EPUB | EPUB |
| Google Play Books | EPUB | EPUB |
| IngramSpark | EPUB | EPUB |
| Draft2Digital | EPUB, DOCX | EPUB |
The pattern is obvious. EPUB everywhere, for everything.
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Frequently Asked Questions
Can I still read old MOBI files on my Kindle?
Yes. Existing MOBI files in your Kindle library remain functional. Amazon still delivers MOBI to very old Kindle devices that can’t handle newer formats. The deprecation only affects uploading new or updated MOBI files to KDP.
Do I need both MOBI and EPUB?
No. EPUB alone covers every retailer, including Amazon. There is no publishing scenario in 2026 that requires creating a MOBI file.
What format does IngramSpark accept for ebooks?
EPUB. IngramSpark requires a properly formatted EPUB file for ebook distribution. They do not accept MOBI, DOCX, or KPF.
Is PDF an ebook format?
Not in any practical sense. PDFs don’t reflow, meaning the text doesn’t adapt to different screen sizes or respond to reader font preferences. They work for print layouts but make terrible ebooks. Every major retailer requires EPUB for ebook distribution.
What’s the difference between EPUB 2 and EPUB 3?
EPUB 2 uses HTML 4.01 and CSS 2.1. EPUB 3 uses HTML5 and CSS3, adding support for embedded multimedia, JavaScript interactivity, advanced accessibility features, and fixed-layout mode. EPUB 3 is the current default and the version you should be creating.
How do I convert a MOBI file to EPUB?
Use Calibre (free). Import the MOBI file, select “Convert books,” choose EPUB as the output format, and Calibre handles the conversion. Review the output carefully, since automated conversion sometimes introduces formatting quirks that need manual cleanup.
Does Amazon’s conversion affect how my book looks?
It can. Amazon converts your EPUB to its internal formats, and the conversion isn’t always pixel-perfect. This is why testing with Kindle Previewer before publishing is essential. Complex layouts, unusual fonts, and heavily styled elements are most likely to shift during conversion.
Should I use Kindle Create or upload an EPUB?
If you publish exclusively on Amazon and want access to Amazon-specific design templates, Kindle Create (which produces KPF files) is a reasonable choice. If you distribute wide, EPUB is better because one file works everywhere. For most authors, EPUB is the safer, more flexible option.