EPUB vs FB2
A detailed comparison of EPUB eBook and FictionBook — 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 filesFictionBook
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 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.
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.
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.
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.
Technical Specifications
| Specification | EPUB | FB2 |
|---|---|---|
| MIME type | application/epub+zip | application/x-fictionbook+xml |
| Extension | .epub | — |
| Container | ZIP archive | Single XML file (optionally zipped) |
| Markup | XHTML 1.1 (EPUB 2); HTML5 (EPUB 3) | — |
| Standards | IDPF/W3C EPUB 2.0.1, 3.0, 3.2, 3.3 | — |
| Extensions | — | .fb2, .fb2.zip |
| Standard | — | FictionBook community spec (maintained on GitHub) |
| Encoding | — | UTF-8 (required) |
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
FB2
- Novel (text only) 200-800 KB
- Novel with cover image 300 KB - 1.5 MB
- Illustrated children's book 5-30 MB
Ready to convert?
Convert between EPUB and FB2 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.
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.
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 FB2. 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 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.