EPUB vs MOBI
A detailed comparison of EPUB eBook and Mobipocket eBook — file size, quality, compatibility, and which format to choose for your workflow.
EPUB 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
Ready to convert?
Convert between EPUB and MOBI online, free, and without installing anything. Encrypted upload, automatic deletion after 2 hours.
Frequently Asked Questions
EPUB (Electronic Publication) is the open standard eBook format maintained by the W3C. It supports reflowable text that adapts to screen size, embedded fonts, images, and interactive content, making it the most widely supported eBook format globally.
MOBI (Mobipocket eBook) is an ebook format designed for reading long-form text on dedicated e-readers, tablets, and ebook apps. It is part of the ebooks family and typically supports reflowable text, embedded images, chapter navigation, cover art, and metadata (title, author, ISBN) in a portable package.
EPUB files open in Apple Books, Google Play Books, Calibre (free), Kobo eReaders, and Adobe Digital Editions. Note that Amazon Kindle does not natively support EPUB, so conversion to MOBI or AZW3 is needed.
Dedicated e-readers — Kindle, Kobo, Nook, Pocketbook — support the most common ebook formats. On phones, Apple Books, Google Play Books, Moon+ Reader and KOReader all handle MOBI. For desktop reading, Calibre is the universal ebook viewer and library manager. Convert to EPUB or PDF for maximum compatibility.
Use EPUB for reading on phones and eReaders since it reflows text to fit any screen. Use PDF for documents with fixed layouts like textbooks with precise formatting, scanned pages, or documents intended for printing.
Upload your MOBI to KaijuConverter and pick EPUB, MOBI, PDF, AZW3, or similar targets. Our Calibre-powered pipeline preserves chapter structure, embedded images, cover art, and metadata. Conversion takes seconds for typical novels; long technical books with many images may take a little longer.