Convert E-books to Any Format
Support for 9 e-book formats. EPUB and FB2 convert in your browser; other formats use optional server processing.
Drop your e-book files here
or click to browse files
What each format does to your book
We converted one e-book into every format this tool offers and measured the result. The source was a 14-chapter book with styled text, a cover and two figures, so the differences below are mostly about how each format treats pictures.
Source: EPUB, 1470.3 KB, 14 chapters, about 9,674 words, a cover and two figures. Converted with Calibre 9.11.
| Format | Type | Output size | vs source | Images kept | Keeps | Verdict |
|---|---|---|---|---|---|---|
| EPUB | Reflowable | 1471.3 KB | 100% | 4 of 4 | Text, styling, images | The safe default |
| AZW3 | Reflowable | 1526.8 KB | 104% | 4 of 4 | Text, styling, images | For modern Kindles |
| MOBI | Reflowable | 1521.8 KB | 104% | 4 of 4 | Text, styling, images | For older Kindles |
| Fixed | 1653.6 KB | 112% | 3 of 4 | Exact appearance | Print, not reading on a phone | |
| FB2 | Reflowable | 2050.1 KB | 139% | 4 of 4 | Text, styling, images | Large: images become text |
| SNB | Reflowable | 610 KB | 41% | 3 of 4 | Text and images | Niche Chinese reader format |
| LRF | Reflowable | 155.2 KB | 11% | 4 of 4 | Text, smaller images | Retired Sony format |
| RB | Reflowable | 1497 KB | 102% | 1 of 4 | Text, most images lost | Obsolete |
| PDB | Reflowable | 14.9 KB | 1% | 0 of 4 | Text only | Drops every picture |
| TXT | Plain text | 53.5 KB | 4% | 0 of 4 | Text only | No formatting at all |
- Every format kept the words. Even the smallest outputs preserved the full text when we converted them back, so a tiny file does not mean a truncated book.
- The size differences come almost entirely from pictures. PDB dropped all four images and landed at 1% of the source, and LRF shrank them to a fraction of their original size at 11%.
- FB2 came out the largest at 139% because it stores images as text inside the XML, which inflates them by about a third.
- For a book you actually want to read, EPUB and AZW3 are the right answers. Both kept the text, the styling and all four images, at 100% and 104% of the source.
Which format should you pick
If you read on a Kindle, choose AZW3. For everything else, from Kobo and Nook to phone and tablet apps, choose EPUB. The older formats on this page are here so you can open books you already have, not because they are worth converting to.
Measured on one representative book with Calibre. Your own results depend mostly on how many images your book contains: a text-only novel will convert to nearly the same size in every format.
Supported E-book Formats
Convert between 9 different formats - from EPUB and MOBI to legacy ebook formats
E-book Formats
The open e-book standard, built on HTML and CSS.
Best for almost every reader except Kindle.
Text reflows to any screen; the safe default.
Amazon's older Kindle format.
Best for older Kindle devices and apps.
Superseded by AZW3, which Amazon now prefers.
Amazon's current Kindle format, also called KF8.
Best for modern Kindles, with better styling than MOBI.
Kept every image in our test, at much the same size as EPUB.
FictionBook, an XML format popular in Russia.
Best for text-only fiction libraries.
Stores pictures as text inside the XML, so files run large.
The retired format from Sony's e-reader line.
Best only for old Sony Readers.
Shrinks images heavily; convert to EPUB instead.
Palm Database, from the PalmPilot era.
Best for very old handheld readers.
Keeps the words but drops pictures entirely.
The Rocket eBook format from the late 1990s.
Best for archival curiosity more than daily use.
Kept the text but lost most images in our test.
A Chinese e-book format used by Shanda Bambook.
Best for that specific reader ecosystem.
Recompresses images, roughly halving the file.
A compressed plain-text format from Psion.
Best for the smallest possible text-only book.
No formatting and no pictures survive.
References
- EPUB 3.3 - W3C Recommendation
- EPUB 3.0 - International Digital Publishing Forum
- Ebook Conversion - calibre User Manual
- Kindle Publishing Guidelines - Amazon KDP
- calibre source repository - GitHub
- FictionBook 2.1 XML Schema - FictionBook.org
- Media types (MIME types) - MDN Web Docs, Mozilla
- ISO 32000-2:2020, Portable document format (PDF 2.0) - ISO