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FB2 → EPUB
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Convert FictionBook format to standard EPUB for wider reader compatibility.
Why this pair exists — FB2 is FictionBook, a popular XML-based open ebook format in Russian-speaking markets. Ergo, the EPUB route. Converting FB2 to EPUB is about reader compatibility more than anything else. Kindle hardware speaks EPUB but not FB2; Kobo reads EPUB happily but stumbles on FB2; third-party apps vary. This tool bridges the gap without asking you to install and learn Calibre yourself. In practice FB2 is FictionBook, a popular XML-based open ebook format in Russian-speaking markets. On the other end, EPUB is the open IDPF ebook standard, a ZIP of HTML and CSS supported by every modern e-reader.
FictionBook
Source formatFictionBook (FB2) is an XML-based eBook format popular in Russia and Eastern Europe. It provides structured semantic markup for fiction and non-fiction books.
EPUB eBook
Target formatEPUB 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.
Why convert FB2 to EPUB
EPUB reflows correctly on the small e-ink screens; some FB2 files are fixed-layout PDFs or early-generation ePubs that do not resize gracefully. Converting fixes the reading experience on 6-inch screens.
HOW TO CONVERT
FB2 → EPUB
Provide the FB2
Select or drag your ebook up to 100 MB. No account or library sign-in is required.
Run Calibre
Our pipeline runs the same Calibre command that powers desktop conversions, with device-appropriate defaults.
Retrieve the EPUB
A download link appears when conversion completes. Metadata is preserved inside the EPUB for library indexing.
Common Use Cases
Share across platforms
Send EPUB files to anyone without worrying about whether they have the right software for FB2.
Embed in documents
Drop EPUB output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
EPUB often produces smaller files than FB2 for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
FB2 vs EPUB — Strengths and limitations
What each format does best, and where it falls short.
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
- No styling, no custom fonts, no fixed layouts.
- Minimal Western-language tooling.
- Kindle and Apple Books do not support FB2 natively.
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.
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.
FB2 vs EPUB — Technical specifications
Side-by-side comparison of the technical details.
FB2
- MIME type
- application/x-fictionbook+xml
- Extensions
- .fb2, .fb2.zip
- Container
- Single XML file (optionally zipped)
- Standard
- FictionBook community spec (maintained on GitHub)
- Encoding
- UTF-8 (required)
EPUB
- MIME type
- application/epub+zip
- Container
- ZIP archive
- Extension
- .epub
- Markup
- XHTML 1.1 (EPUB 2); HTML5 (EPUB 3)
- Standards
- IDPF/W3C EPUB 2.0.1, 3.0, 3.2, 3.3
| Specification | FB2 | EPUB |
|---|---|---|
| MIME type | application/x-fictionbook+xml | application/epub+zip |
| Extensions | .fb2, .fb2.zip | — |
| Container | Single XML file (optionally zipped) | ZIP archive |
| Standard | FictionBook community spec (maintained on GitHub) | — |
| Encoding | UTF-8 (required) | — |
| Extension | — | .epub |
| Markup | — | XHTML 1.1 (EPUB 2); HTML5 (EPUB 3) |
| Standards | — | IDPF/W3C EPUB 2.0.1, 3.0, 3.2, 3.3 |
FB2 vs EPUB — Typical file sizes
Approximate file sizes for common scenarios.
FB2
- Novel (text only) 200-800 KB
- Novel with cover image 300 KB - 1.5 MB
- Illustrated children's book 5-30 MB
EPUB
- Novel (300 pages, text only) 200-800 KB
- Illustrated reference book 5-30 MB
- Fixed-layout children's book 30-100 MB
Quality & Compatibility
Cover images are re-embedded at the device-appropriate resolution, which may compress them more aggressively than the FB2 did. If you need pixel-perfect covers, override the cover image in Advanced to skip the re-encode.
Tips for Best Results
- Always keep the FB2 original until you have verified the EPUB on the destination device — screenshots in a browser can look fine while e-ink rendering differs.
- For large libraries, batch-convert via a single ZIP upload; the job processes each ebook individually and returns a combined archive.
- Set the output profile (Kindle, Kobo, generic) in Advanced — defaults are sensible but a device-specific profile yields better reflow.
Frequently Asked Questions
Yes. The free tier accepts files up to 25 MB without registration, email capture or watermarks; paid plans go up to 2 GB. Paid plans raise the size cap, enable batch conversions and provide a REST API for automation, but nothing on the free tier is quality-limited — the output is exactly the same as on any paid plan.
Yes, provided the FB2 itself has a well-formed ToC. Calibre reads the navigation structure and writes an equivalent ToC into the EPUB. If the source lacks a ToC we can generate one from heading levels in Advanced → structure detection.
Uploads run over HTTPS, files are processed in isolated containers, and both the source FB2 and the EPUB output are auto-deleted within two hours. No account is required, file contents are never logged, and KaijuConverter does not use uploads for AI training. The paid plan adds a signable data-processing agreement for regulated workflows.
No. KaijuConverter does not strip digital rights management. DRM-free FB2 files — anything you authored yourself, public-domain classics, files from DRM-free retailers — convert without any restriction.
Most files finish in well under a minute. Small images and documents are typically ready in a few seconds; large video or audio files scale roughly with duration. Upload speed from your network is usually the dominant factor, not server time.
Yes. The cover is extracted from the FB2 and re-embedded in the EPUB at device-appropriate dimensions. You can also override it in Advanced by uploading a custom cover image alongside the book file.
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Read guideSecure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.