CONVERT EPUB → FB2 (EPUB to FB2)
Fast, secure EPUB to FB2 conversion. No registration required.
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Ghostscript + QPDFHOW TO CONVERT EPUB → FB2
Upload the EPUB
Drop the ebook file into the uploader. We detect the format and extract metadata automatically.
Convert through Calibre
Calibre parses the EPUB structure, reflows content and writes a FB2 with the appropriate CSS profile for the target readers.
Download the FB2
Grab the converted ebook; both files auto-delete within two hours of the job finishing.
Here is the short version — EPUB is the open IDPF ebook standard, a ZIP of HTML and CSS supported by every modern e-reader. Hence the need for FB2. Our EPUB to FB2 converter uses the same Calibre engine that powers the bulk of the ebook world. Authors use it, bookstores use it, pirates (unfortunately) use it — it is the de-facto standard for ebook format conversion and we just expose it over a simple browser upload. Technical note: EPUB is the open IDPF ebook standard, a ZIP of HTML and CSS supported by every modern e-reader. Compare that with FB2 is FictionBook, a popular XML-based open ebook format in Russian-speaking markets.
Why convert EPUB to FB2
FB2 works on your specific reader where EPUB does not. Ebook formats are tied to ecosystems — FB2 is Amazon-native, FB2 is IDPF-standard and opens everywhere, pick the one that matches your device and convert the rest.
EPUB vs FB2 — Technical specifications
Side-by-side comparison of the technical details.
EPUB
- MIME type
- application/epub+zip
- Extension
- .epub
- Container
- ZIP archive
- Markup
- XHTML 1.1 (EPUB 2); HTML5 (EPUB 3)
- Standards
- IDPF/W3C EPUB 2.0.1, 3.0, 3.2, 3.3
- MIME Type
- application/epub+zip
- Category
- eBooks
- Full Name
- EPUB eBook
- Conversion Engine
- CALIBRE
FB2
- MIME type
- application/x-fictionbook+xml
- Extension
- .fb2
- Container
- Single XML file (optionally zipped)
- MIME Type
- application/x-fictionbook+xml
- Category
- eBooks
- Full Name
- FictionBook
- Conversion Engine
- CALIBRE
- Extensions
- .fb2, .fb2.zip
- Standard
- FictionBook community spec (maintained on GitHub)
- Encoding
- UTF-8 (required)
| Specification | EPUB | FB2 |
|---|---|---|
| MIME type | application/epub+zip | application/x-fictionbook+xml |
| Extension | .epub | .fb2 |
| 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 | — |
| MIME Type | application/epub+zip | application/x-fictionbook+xml |
| Category | eBooks | eBooks |
| Full Name | EPUB eBook | FictionBook |
| Conversion Engine | CALIBRE | CALIBRE |
| Extensions | — | .fb2, .fb2.zip |
| Standard | — | FictionBook community spec (maintained on GitHub) |
| Encoding | — | UTF-8 (required) |
EPUB vs FB2 — Strengths and limitations
What each format does best, and where it falls short.
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 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.
Quality & Compatibility
Text content is preserved losslessly — every word of the EPUB ends up in the FB2. Formatting richness depends on what the FB2 container supports; heavy typography that works in EPUB may degrade gracefully in FB2, never lost entirely.
Tips for Best Results
- Set author and title metadata in Advanced before conversion; fixing it after sideloading to a reader is far more work.
- If chapter navigation feels off in the FB2, the source EPUB probably had a weak ToC — Calibre respects what it finds, it cannot invent structure that was not there.
- For fixed-layout EPUB (art books, technical manuals with diagrams) consider whether a reflowable FB2 actually makes sense before converting.
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 EPUB itself has a well-formed ToC. Calibre reads the navigation structure and writes an equivalent ToC into the FB2. 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 EPUB and the FB2 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 EPUB 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 EPUB and re-embedded in the FB2 at device-appropriate dimensions. You can also override it in Advanced by uploading a custom cover image alongside the book file.
EPUB eBook
Source 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.
FictionBook
Target 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.
Going the other way? Convert FB2 back to EPUB with the same engine.
Common Use Cases
Share across platforms
Send FB2 files to anyone without worrying about whether they have the right software for EPUB.
Embed in documents
Drop FB2 output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
FB2 often produces smaller files than EPUB 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.
EPUB vs FB2 — Typical file sizes
Approximate file sizes for common scenarios.
- Novel (300 pages, text only) 200-800 KB
- Illustrated reference book 5-30 MB
- Fixed-layout children's book 30-100 MB
- Novel (text only) 200-800 KB
- Novel with cover image 300 KB - 1.5 MB
- Illustrated children's book 5-30 MB
Sensitive Documents, Scanned OCR, or 500+ Pages?
For legally sensitive archives that must never leave your local network, or multi-hundred page scanned PDFs needing optical character recognition, local document workstations ensure full compliance.
One-time payment with zero recurring commitment: convert files up to 1 GB, OCR, PDF/A, and .ZIP batches for 24 hours.
Full 7 days of unlimited conversions, up to 2 GB per file, 100% ad-free with zero subscription.
High-throughput enterprise pipeline for files up to 2,048 MB, 50-file batches, ISO PDF/A, and priority processing.
Offline conversion for multi-hundred page contracts, spreadsheets, and local optical extraction.
High-accuracy legal OCR, certified PDF/A archiving, and compliant document redaction.
Related comparisons
See these formats side by side to understand which fits your use case best.
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