About MOBI Files
Mobipocket eBook
MOBI 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.
Family
eBooks
Extension
.mobi
MIME Type
application/x-mobipocket-ebook
Can Use As
HOW MOBI
CAME TO BE.
MOBI was developed by Mobipocket, a French software company founded in 2000 by Thierry Brethes and Nathalie Ting. Their ebook reader ran on Palm devices, Pocket PCs, Symbian phones, and later BlackBerry. The format was a PalmDOC-based container using compressed HTML — elegantly simple for the hardware of its day.
Amazon bought Mobipocket in April 2005 and used MOBI as the direct ancestor of AZW when the first Kindle launched in November 2007. For a decade MOBI was the lingua franca of pre-Kindle ereaders. Amazon stopped accepting MOBI uploads to Kindle Direct Publishing in 2022 (EPUB is now preferred), effectively ending MOBI’s commercial life. Calibre and other tools still produce MOBI for legacy devices.
CURIOSITIES &
TRIVIA.
Amazon's first Kindle (2007) ran MOBI files internally — AZW was just MOBI with added DRM.
Amazon bought Mobipocket in 2005 specifically to own the ebook format they would build the Kindle on.
A MOBI file uses Palm Database (PDB) containers — the same structure as Palm Pilot apps from the 1990s.
Every Kindle device reads MOBI out of the box, even if Amazon has stopped shipping it.
Kindle Direct Publishing stopped accepting MOBI uploads in August 2022 — EPUB is now the required submission format.
STRENGTHS &
LIMITATIONS.
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
- 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.
Typical Sizes & Weights
Text-only novel
200 KB - 1 MB
Illustrated book
2-10 MB
Technical Specifications
- MIME type
- application/x-mobipocket-ebook
- Extension
- .mobi, .prc (PalmDOC variant)
- Container
- Palm Database (PDB)
- Markup
- Compressed HTML subset
- Successor
- .azw, .azw3 (Kindle-specific)
CONVERT FROM
MOBI
Common Use Cases
Older Kindle devices, legacy eBook collections.
Related Formats
Popular comparisons
MOBI vs PDF
Differences, file size, and when to choose each format.
MOBI vs EPUB
Differences, file size, and when to choose each format.
MOBI vs DOCX
Differences, file size, and when to choose each format.
MOBI vs TXT
Differences, file size, and when to choose each format.
MOBI vs HTML
Differences, file size, and when to choose each format.
MOBI vs FB2
Differences, file size, and when to choose each format.
Popular MOBI conversions
The most-requested destinations when starting from MOBI.
Frequently Asked Questions about MOBI
Frequently Asked Questions
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.
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.
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.
EPUB is the open ebook standard — it plays on every e-reader except older Kindles and in every major ebook app. PDF is better for fixed-layout content (textbooks, coffee-table books) and printing. Pick EPUB when the ebook is reflowable text, PDF when the layout matters more than the reading experience.