EPUB vs MOBI
A detailed comparison of EPUB eBook and Mobipocket eBook — file size, quality, compatibility, and which format to choose for your workflow.
Short answer: use EPUB for everything except old Kindle devices (pre-2024 models), where MOBI is still the safest format. EPUB is the open international standard for ebooks; MOBI is Amazon's legacy proprietary format that the company itself has been phasing out since 2022.
If you're publishing or sharing ebooks today, EPUB is the right answer 95% of the time. The only meaningful reason to still produce MOBI files is if you have readers using a Kindle from before late 2022 (when Amazon switched to AZW3/KFX as the default). For everything modern — new Kindles, Kobo, Apple Books, Google Play Books, Calibre, Adobe Digital Editions — EPUB is what you want.
EPUB vs MOBI at a glance
| Dimension | EPUB | MOBI |
|---|---|---|
| Standard | Open (IDPF / W3C) | Proprietary (Amazon) |
| Released | 2007 (EPUB 2), 2011 (EPUB 3) | 2000 (Mobipocket Reader) |
| File extension | .epub | .mobi, .prc, .azw |
| Underlying tech | XHTML + CSS + XML (zipped) | PalmDOC + HTML (legacy) |
| Device support | Universal except old Kindles | Mainly older Kindles |
| Reflowable text | ✅ Yes (responsive layout) | ✅ Yes |
| Fixed layout | ✅ Supported (EPUB 3 FXL) | ⚠️ Limited |
| Audio/video embed | ✅ Native (EPUB 3) | ❌ No |
| Interactive features | ✅ JavaScript supported | ❌ No |
| DRM | Adobe ADEPT, LCP (optional) | Amazon DRM (most files) |
| Future-proof | ✅ Active W3C standard | ⚠️ Deprecated by Amazon (2022) |
When should you use EPUB vs MOBI?
EPUB Use when…
- Publishing a new ebook in 2026 — EPUB is the universal format. Every retailer (except the Amazon Kindle Direct Publishing input flow, which converts internally to KFX/AZW3) accepts and prefers EPUB.
- Sharing books across multiple devices — A reader with iPhone + iPad + Mac + Kobo can read the same EPUB file on all four. MOBI works on none of them.
- Modern Kindles (2022+) — Amazon now accepts EPUB directly via Send-to-Kindle. The conversion to KFX happens server-side, transparent to you.
- Self-publishing on Apple Books, Google Play Books, Kobo, Barnes & Noble — All require EPUB.
- Library lending (OverDrive, Libby) — Distributes EPUB with DRM.
- Anything with audio, video, or interactivity — EPUB 3 supports embedded media; MOBI doesn't.
- Academic textbooks with complex layout — EPUB 3 Fixed Layout (FXL) handles multi-column, footnotes, math (MathML), and margin notes properly.
- Open, future-proof archive — EPUB is an open W3C standard. MOBI is proprietary and being phased out.
MOBI Use when…
- Old Kindle devices (pre-2022) — Original Kindle, Kindle 2, Kindle 3, Kindle DX, and early Paperwhites only natively support MOBI/AZW. They can't read EPUB without conversion.
- Sending personal documents to legacy Kindles via email — Amazon's Send-to-Kindle accepted MOBI for years; if you have a workflow built around
.mobiattachments to your@kindle.comaddress and the recipient is on an old device, MOBI still works. - Backwards compatibility with Mobipocket Reader software — Some niche enterprise workflows (technical manuals, older ebook libraries) still use the Mobipocket reader, which requires MOBI.
- Archive of legacy Amazon purchases — Books bought from Amazon before ~2014 were often delivered as MOBI/AZW3. If you've stripped DRM from old purchases for personal backup, those files are MOBI-format by default.
Why almost no one should produce new MOBI files in 2026: Amazon officially deprecated MOBI as a Send-to-Kindle input format in late 2022. New Kindle devices read EPUB natively. The KDP publishing platform converts everything to its internal KFX format. Producing fresh MOBI is solving a problem that no longer exists for ~95% of readers.
Best format by use case
Self-publishing in 2026
Every modern store wants EPUB. KDP converts EPUB to KFX automatically.
Winner: EPUBiPhone / iPad / Android
Apple Books, Google Play Books, Kobo all use EPUB. MOBI requires conversion.
Winner: EPUBOld Kindle (pre-2022)
Native format. EPUB requires Send-to-Kindle conversion or third-party tools.
Winner: MOBIAcademic / textbooks
EPUB 3 FXL handles multi-column, MathML, footnotes properly.
Winner: EPUBMultimedia ebooks
Audio/video embedding is native in EPUB 3. MOBI doesn't support it.
Winner: EPUBLong-term archive
Open W3C standard guarantees future readability. MOBI is being phased out.
Winner: EPUBLibrary lending (OverDrive)
OverDrive distributes ePub files with optional Adobe DRM.
Winner: EPUBEmail to old Kindle
Pre-2022 Kindles handle .mobi attachments natively without conversion.
Winner: MOBIEPUB eBook
eBooksEPUB is the open standard for reflowable digital books. It adapts text to any screen size and is supported by most e-readers except Kindle. EPUB 3 adds support for multimedia and interactivity.
About EPUB filesMobipocket eBook
eBooksMOBI is the Mobipocket eBook format historically used by Amazon Kindle devices. While Amazon has moved to newer formats, MOBI remains relevant for older Kindles and legacy eBook libraries.
About MOBI filesStrengths Comparison
EPUB Strengths
- Open standard — no vendor lock-in, no DRM required.
- Reflowable text — adapts to any screen size, font size, or orientation.
- Rich typography via CSS, embedded fonts, and SVG.
- Accessibility-first: native support for screen readers, adjustable text, and alt-text.
- Universal across every non-Kindle ebook reader and library app.
MOBI Strengths
- Universal Kindle support on every device ever released.
- Very small file sizes for text-heavy books.
- Mature tooling via Calibre and Amazon's KindleGen.
- Simple container structure — easy to parse.
Limitations
EPUB Limitations
- Kindle does not support EPUB natively (Amazon wants you to convert to AZW3).
- Fixed-layout EPUBs (for children's books, comics) are awkward to author.
- Rendering quality varies between apps — some CSS works everywhere, some does not.
- Adobe DRM (ADEPT) or Apple FairPlay are optional layers that complicate portability.
MOBI Limitations
- Deprecated by Amazon for new uploads since 2022.
- Poor support for rich typography (drop caps, ligatures, fixed layout).
- No embedded fonts in the base format.
- Proprietary container discouraged use outside Kindle.
- Effectively a legacy format — new books go to AZW3/EPUB.
Technical Specifications
| Specification | EPUB | MOBI |
|---|---|---|
| MIME type | application/epub+zip | application/x-mobipocket-ebook |
| Extension | .epub | .mobi, .prc (PalmDOC variant) |
| Container | ZIP archive | Palm Database (PDB) |
| Markup | XHTML 1.1 (EPUB 2); HTML5 (EPUB 3) | Compressed HTML subset |
| Standards | IDPF/W3C EPUB 2.0.1, 3.0, 3.2, 3.3 | — |
| Successor | — | .azw, .azw3 (Kindle-specific) |
Typical File Sizes
EPUB
- Novel (300 pages, text only) 200-800 KB
- Illustrated reference book 5-30 MB
- Fixed-layout children's book 30-100 MB
MOBI
- Text-only novel 200 KB - 1 MB
- Illustrated book 2-10 MB
Technical deep dive: EPUB vs MOBI
What's inside an EPUB file
EPUB is essentially a ZIP archive with a specific internal structure. Rename a .epub to .zip, unzip it, and you'll find:
mimetype— single line:application/epub+zipMETA-INF/container.xml— points to the package fileOEBPS/content.opf— the manifest (list of all files + reading order)OEBPS/toc.ncx(EPUB 2) ornav.xhtml(EPUB 3) — table of contentsOEBPS/Text/— XHTML files, one per chapterOEBPS/Styles/— CSS stylesheetsOEBPS/Images/— illustrations, cover
This structure means EPUB is just web tech repackaged — XHTML, CSS, optional JavaScript. Any developer who can build a website can build an EPUB by hand. This is also why every modern reader (which is fundamentally a stripped-down browser) handles EPUB natively.
What's inside a MOBI file
MOBI is based on PalmDOC (PDB format) from the original PalmPilot ebook ecosystem. Internally:
- A header section with metadata
- Compressed HTML body (custom Mobipocket compression — a variant of LZ)
- Image data appended after the text
- Optional DRM headers (for Amazon-purchased books)
There are actually three MOBI variants in the wild that all use the .mobi or .azw extension:
- MOBI (original) — PalmDOC compression, basic HTML
- AZW — Amazon's first DRM-wrapped MOBI variant (2007-2011)
- AZW3 / KF8 — Amazon's modernized format (2011-2022) with CSS3 support, fixed layout, embedded fonts. Better than original MOBI but still proprietary.
Modern Kindles (2022+) use KFX internally, a completely different format that's not directly compatible with old MOBI/AZW3 readers.
Compatibility matrix (2026)
| Reader | EPUB | MOBI | AZW3 | KFX |
|---|---|---|---|---|
| Kindle Paperwhite (2024+) | ✅ Native | ✅ Legacy | ✅ Legacy | ✅ Native |
| Kindle (pre-2022) | ❌ Convert needed | ✅ Native | ✅ Native | ❌ Not supported |
| Kobo (all models) | ✅ Native | ❌ Convert needed | ❌ | ❌ |
| Apple Books (iOS/macOS) | ✅ Native | ❌ | ❌ | ❌ |
| Google Play Books | ✅ Native | ❌ | ❌ | ❌ |
| Barnes & Noble Nook | ✅ Native | ❌ | ❌ | ❌ |
| Calibre (PC) | ✅ Native | ✅ Native | ✅ Native | ❌ Plugin needed |
| Adobe Digital Editions | ✅ Native | ❌ | ❌ | ❌ |
Conversion considerations
Converting EPUB → MOBI is straightforward and lossless for text. Calibre, KindleGen, and our free EPUB-to-MOBI converter all do it well. Some EPUB 3 features (audio, video, interactive scripts) are dropped because MOBI doesn't support them.
Converting MOBI → EPUB is also generally clean. The HTML inside MOBI gets re-wrapped as XHTML, the table of contents is rebuilt, and you get a modern EPUB file. Our MOBI-to-EPUB converter handles this without needing Calibre installed.
One exception: if your MOBI file has Amazon DRM (which most purchased Kindle books do), neither converter can read it. DRM removal is a legally gray area and requires separate tools — out of scope here.
What about AZW3 specifically?
AZW3 is essentially "MOBI 2.0" — same underlying PalmDOC structure but with CSS3 support, embedded fonts, and fixed-layout features. If you have an .azw3 file from an old Kindle purchase, it's much closer in capability to EPUB 3 than to original MOBI. Some converters treat .mobi and .azw3 as the same format; technically they're not, but practically the differences only matter for advanced layout work.
For 2026 publishing: make EPUB your master format, convert to MOBI/AZW3 only on demand for old-Kindle readers.
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Convert between EPUB and MOBI online, free, and without installing anything. Encrypted upload, automatic deletion after 60 minutes.
Frequently Asked Questions
Yes. Since late 2022, all Amazon Kindle devices (and the Kindle apps on iOS/Android/Mac/PC) accept EPUB natively. Send-to-Kindle (the email-to-Kindle service) also accepts EPUB directly. Internally Amazon converts to its KFX format, but that's transparent — you just send the EPUB and the book appears on the device.
For new content, essentially yes. Amazon stopped accepting MOBI through Send-to-Kindle in late 2022. KDP (the self-publishing platform) accepts EPUB and DOCX, not MOBI. New Kindle devices read EPUB natively. The only place MOBI still actively matters is on Kindle devices manufactured before 2022 that haven't been updated, and in archived copies of older Amazon purchases.
Each reader has its own CSS rendering quirks. EPUB is built on web tech (XHTML + CSS), so just like websites render slightly differently across browsers, EPUBs render slightly differently across readers. Common issues: fonts substituted, line spacing changes, page breaks shifted. To minimize: stick to EPUB 3 spec, test in Calibre and Apple Books before publishing, avoid exotic CSS features.
Yes — most converters preserve the table of contents, chapter divisions, and metadata. The HTML inside MOBI is re-wrapped as XHTML and the TOC is rebuilt from the existing chapter markers. Our converter does this automatically. Quality is usually identical to the source MOBI, just in EPUB packaging.
Yes, optionally. Two main DRM systems are used: Adobe ADEPT (used by Adobe Digital Editions, Kobo, OverDrive libraries) and Readium LCP (newer, more open). Both wrap the EPUB and require authorization to open. Most self-published EPUBs are sold without DRM.
AZW3 (also called KF8) is Amazon's 2011 modernization of MOBI. Same underlying PalmDOC structure, but adds CSS3 support, embedded custom fonts, fixed layout, and SVG. AZW3 is to MOBI what EPUB 3 is to EPUB 2 — same family, much more capable. Most "MOBI" files distributed in the last 10 years are actually AZW3 with a .mobi extension.
Not natively. iPhone (Apple Books) only reads EPUB. To read MOBI on iPhone you need a third-party app (Kindle app reads Amazon-format files; KyBook, Marvin, or other readers handle MOBI directly), or you convert the MOBI to EPUB first.
EPUB 3 unless you have a specific reason to target very old readers. EPUB 3 supports HTML5, CSS3, JavaScript, audio/video, MathML, and fixed-layout. Every reader from the past 10 years handles EPUB 3 fine. EPUB 2 is the older 2007 spec — still works, but no reason to choose it for new content.