EPUB (Electronic Publication) is the open ISO/IEC standard for eBooks, maintained by the W3C. EPUB 3 (the current version) is essentially a ZIP file containing HTML5, CSS3, and media assets. It supports reflowable text, fixed-layout documents, multimedia, and MathML. EPUB is the native format for Kobo, Apple Books, Nook, Google Play Books, and most non-Kindle eReaders. It is the best choice for maximum compatibility across platforms.
Free eBook Converter — Online
Convert EPUB, MOBI & AZW to Any eBook Format
Convert eBooks between EPUB, MOBI, AZW3, PDF, DOCX, and TXT using Calibre — the world's most comprehensive open-source eBook management library.
EPUB, MOBI & AZW3 support
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Metadata & TOC preserved
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Up to 100 MB free • Outputs: EPUB, MOBI, PDF, TXT
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How to Use eBook Converter
Convert your files in three simple steps — no software, no signup.
01
Upload Your eBook
Drop an EPUB, MOBI, AZW, AZW3, or PDF file. Files from Kindle, Kobo, or any eReader are supported.
02
Choose Output Format
Select EPUB for universal compatibility, MOBI/AZW3 for Kindle, PDF for printing, or TXT for plain text extraction.
03
Download Converted eBook
Your eBook is converted via Calibre with metadata, table of contents, and chapter structure intact.
Features
Why Use eBook Converter?
All Major eBook Formats
EPUB 2 & 3, MOBI, AZW, AZW3 (Kindle Format 8), FB2, LIT, LRF, PDB, and more — Calibre handles them all.
Table of Contents
The original table of contents and chapter structure is preserved in the converted output for easy navigation.
Metadata Preserved
Title, author, publisher, language, and cover image metadata are transferred to the output format.
Kindle & Kobo Ready
Convert to AZW3/MOBI for Kindle devices, or EPUB for Kobo, Nook, Apple Books, and any standards-compliant reader.
Private Conversion
eBook files are processed in a sandboxed session and deleted within 2 hours. We never store or index content.
Powered by Calibre
Calibre is the industry-standard open-source eBook tool used by millions worldwide for format conversion and library management.
Compatibility
Supported Formats
All the formats you need, all in one place.
| Format | Description | Extension | Best Used For |
|---|---|---|---|
| EPUB | Open eBook standard (IDPF) | .epub |
Kobo, Nook, Apple Books, most readers |
| MOBI | Legacy Mobipocket format (pre-KF8) | .mobi |
Old Kindle devices, Mobipocket reader |
| AZW3 | Kindle Format 8 (modern Kindle) | .azw3 |
Modern Kindle devices (Paperwhite, Oasis) |
| FB2 | FictionBook 2 (Russian e-readers) | .fb2 |
PocketBook, Russian-market e-readers |
| Converted to print-friendly PDF | .pdf |
Printing, archiving, desktop reading | |
| DOCX | Word document from eBook content | .docx |
Editing eBook content in Word |
| TXT | Plain text extraction from eBook | .txt |
Text analysis, NLP, quoting content |
| RTF | Rich Text Format output | .rtf |
Cross-platform word processor editing |
FAQ
Frequently Asked Questions
No. DRM (Digital Rights Management) protected eBooks cannot be converted — this is both a legal restriction and a technical one. Only DRM-free eBooks can be converted.
MOBI is the older Mobipocket format used by early Kindle devices. AZW3 (also known as KF8, Kindle Format 8) is the modern Kindle format that supports advanced CSS, embedded fonts, and enhanced media.
Yes. The embedded cover image is extracted and re-embedded in the output format. For PDF output the cover appears as the first page.
Yes — Calibre converts PDF to EPUB by extracting text and attempting to infer structure. Results vary depending on the PDF: reflowable text PDFs work well; scanned or heavily formatted PDFs may produce irregular output.
Yes. Calibre parses the original TOC structure and rebuilds it for the target format. EPUB3 outputs include both inline and NCX/NAV navigation documents.
Yes — use the "Output Profile" and "Custom CSS" options in the converter options panel to adjust font size, line spacing, and margins for PDF and EPUB output.
Real-World Uses
Who Uses eBook Converter?
From everyday users to professionals — see how people rely on this tool every day.
Kindle Reader
Convert EPUB to Kindle Format
Convert any DRM-free EPUB to AZW3/MOBI to read on Kindle Paperwhite, Oasis, or any Kindle device.
eReader User
Convert MOBI to EPUB for Kobo
Convert MOBI eBooks to EPUB for reading on Kobo, Nook, Apple Books, or any standards-compliant eReader.
Author / Publisher
Edit eBook Content in Word
Convert an EPUB or MOBI to DOCX to extract and edit the text content in Microsoft Word for revision or repurposing.
Educator
Print an eBook as PDF
Convert digital textbooks to PDF for printing, annotation, or distribution to students in a print-based learning environment.
Developer
Integrate eBook Content into Apps
Convert EPUB to TXT to extract clean text for content aggregators, reading apps, or accessibility tools.
Translator
Extract eBook Text for Translation
Convert eBooks to DOCX or TXT to work with professional CAT tools (SDL Trados, Phrase) for book translation projects.
Why TransmuteBox?
TransmuteBox vs. Alternatives
See how we compare to desktop software and other online converters.
| Feature |
Our Tool TransmuteBox |
Calibre App | Other Online |
|---|---|---|---|
| EPUB, MOBI, AZW3 input | Limited | ||
| Converts to Kindle AZW3/MOBI | Limited | ||
| Converts to EPUB | |||
| Converts to PDF | |||
| Metadata & cover preserved | Varies | ||
| Table of contents preserved | |||
| No DRM bypass (legal) | |||
| Free to use | Varies |
Under the Hood
Technical Specifications
Built on industry-standard open-source tools for maximum quality and reliability.
Limits & Restrictions
- Max file size: 100 MB (free)
- No DRM-protected files supported
- Input: EPUB, MOBI, AZW, AZW3, FB2, PDF, DOCX
Calibre
EPUB
MOBI
AZW3
Kindle
eBook
Kobo
Conversion Engine
Calibre 6.x ebook-convert CLI — the world's most comprehensive open-source eBook converter
Output Quality
Full metadata + TOC preservation · cover image extracted and re-embedded · chapter structure maintained
Average Speed
Typical: 5–15 s per eBook; large PDFs to EPUB may take 20–30 s
Data Security
HTTPS transfer · isolated temp dir · auto-purged in 2 h
Input formats
EPUB, MOBI, AZW, AZW3, FB2, LIT, PDF, DOCX, TXT
Output formats
EPUB, MOBI, AZW3, PDF, DOCX, TXT, RTF, FB2
Metadata
Title, author, publisher, language, cover preserved
Complete Guide
eBook Formats Explained: EPUB, MOBI, AZW3, and Why Format Matters for Your Device
eBook formats differ in more than just file extension — they determine which devices can read the file, whether the text reflows on small screens, and what features like fonts and tables are supported.
EPUB: The Open Standard
MOBI and AZW3: The Kindle Formats
MOBI (Mobipocket) is the older Kindle format — limited in CSS support and based on the PalmDOC structure. AZW3 (Kindle Format 8) is the modern replacement, supporting HTML5, advanced CSS, embedded fonts, and more complex layouts. Modern Kindle devices (Paperwhite, Oasis, Scribe) read both MOBI and AZW3 natively. For sideloading personal eBooks, AZW3 is preferred; MOBI is retained for older devices and Mobipocket reader apps.
How Calibre Handles Conversion
Calibre's ebook-convert utility parses the source format's internal structure, extracting the text flow, images, CSS, TOC structure, and metadata. It then reconstructs these elements in the target format's container. Some features translate directly (chapter headings, images, tables) while others require adaptation (fixed-layout EPUB becomes reflowable in MOBI). Calibre provides extensive CSS override options for fine-tuning the visual output.
Converting PDF to EPUB: Expectations
PDF-to-EPUB conversion is the most challenging direction because PDFs are designed for fixed-page presentation, not reflowable reading. Calibre uses heuristics to detect paragraph boundaries, headings, and columns, but results vary significantly. PDFs with clean text flows (like a novel or report) convert reasonably well. PDFs with complex multi-column layouts, tables, or heavy use of positioned text blocks often produce irregular EPUB output. For these, manual cleanup in a EPUB editor is recommended.
DRM and Legal Considerations
DRM (Digital Rights Management) protects commercially purchased eBooks from being converted or redistributed. Circumventing DRM — even for personal use — is illegal in many jurisdictions under laws like the DMCA (USA) and the EU Copyright Directive. TransmuteBox does not support or enable DRM removal. Only DRM-free eBooks — such as those purchased from stores that offer DRM-free options, or your own authored content — can be converted.