FB2 vs MOBI
A detailed comparison of FictionBook and Mobipocket eBook — file size, quality, compatibility, and which format to choose for your workflow.
FictionBook
eBooksFictionBook (FB2) is an XML-based eBook format popular in Russia and Eastern Europe. It provides structured semantic markup for fiction and non-fiction books.
About FB2 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
FB2 Strengths
- Pure XML — trivial to parse, search, and transform.
- Single-file ebooks with inline images.
- Excellent on low-powered e-readers.
- De-facto standard in Russian-language ebook ecosystem.
- Simple structure makes conversion to any other format straightforward.
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
FB2 Limitations
- No styling, no custom fonts, no fixed layouts.
- Minimal Western-language tooling.
- Kindle and Apple Books do not support FB2 natively.
- Non-fiction with complex typography (textbooks, cookbooks) is a poor fit.
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 | FB2 | MOBI |
|---|---|---|
| MIME type | application/x-fictionbook+xml | application/x-mobipocket-ebook |
| Extensions | .fb2, .fb2.zip | — |
| Container | Single XML file (optionally zipped) | Palm Database (PDB) |
| Standard | FictionBook community spec (maintained on GitHub) | — |
| Encoding | UTF-8 (required) | — |
| Extension | — | .mobi, .prc (PalmDOC variant) |
| Markup | — | Compressed HTML subset |
| Successor | — | .azw, .azw3 (Kindle-specific) |
Typical File Sizes
FB2
- Novel (text only) 200-800 KB
- Novel with cover image 300 KB - 1.5 MB
- Illustrated children's book 5-30 MB
MOBI
- Text-only novel 200 KB - 1 MB
- Illustrated book 2-10 MB
Ready to convert?
Convert between FB2 and MOBI online, free, and without installing anything. Encrypted upload, automatic deletion after 60 minutes.
Frequently Asked Questions
FB2 (FictionBook) 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.
FB2 (FictionBook) is an ebook formato designed para reading long-form text on dedicated e-readers, tablets, e ebook apps. It is part of the ebooks family e tipicamente suporta reflowable text, embedded images, chapter navigation, cover art, e metadata (title, author, ISBN) em um 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 FB2. For desktop reading, Calibre is the universal ebook viewer and library manager. Convert to EPUB or PDF for maximum compatibility.
Dedicated e-readers — Kindle, Kobo, Nook, Pocketbook — support the most common ebook formatoos. On phones, Apple Books, Google reproduzir Books, Moon+ Reader e KOReader all handle FB2. para desktop reading, Calibre is the universal ebook viewer e library manager. converter to EPUB ou PDF para máximo compatibilidade.
Upload your FB2 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.