EPUB size guide
Send to Kindle file too large?
Amazon’s web uploader currently advertises support for files up to 200 MB. If an EPUB exceeds the route’s limit—or simply takes too long—reduce its real payload, not just the filename.
Find what consumes the space
An EPUB is a ZIP archive, so its total size hides the cause. Make a copy, inspect the archive and sort files by uncompressed size. In most oversized books, high-resolution photographs, scanned pages, duplicate images or embedded font families dominate. XHTML and CSS are rarely the main problem.
Resize images for the reading use
A 6000-pixel camera image may add megabytes while providing little visible benefit on an e-reader. Resize images to a sensible reading resolution, keep the aspect ratio, and use appropriate compression. Photographs are usually smaller as JPEG; line art and transparency may require PNG. Do not convert every image blindly.
Remove true duplicates carefully
Some exports include the same cover or illustration under several names. Before removing one, search the OPF manifest, XHTML, CSS and navigation resources for references. Deleting the “extra” file without updating those references creates a smaller but invalid book.
Review embedded fonts
A full font family can be larger than the text. Keep only weights and styles actually used, and make sure you have permission to embed or modify the font. Removing fonts requires updating both CSS and the OPF manifest. If the book depends on specialist glyphs, test every relevant script and symbol afterward.
Do not repeatedly ZIP the EPUB
Putting an EPUB inside another ZIP does not make it a smaller EPUB that Kindle can process. The service needs the actual .epub package. Recompressing already compressed JPEG or font files also yields little benefit and can break EPUB packaging rules if done with a generic archiver.
Protect the cover: the cover is a high-value image. Optimize it conservatively, preserve its manifest item, and keep the EPUB 3 cover-image property and EPUB 2 compatibility reference pointed at the final file.
Validate after every size reduction
- Keep the untouched original.
- Change one resource group at a time.
- Update paths, media types and CSS references.
- Rebuild the EPUB correctly.
- Open several chapters and the table of contents.
- Confirm the cover and special characters.
- Run EPUB validation before uploading.
When size is not the real problem
If the file is comfortably below the displayed limit but still fails after upload, inspect its structure. A broken manifest or malformed XML will not be fixed by shaving a few megabytes. Likewise, if several small files fail, check the service, browser and account.
Reduced the file? Check the package
FixMyEPUB verifies common cover and delivery references after your edits, privately in the browser.
Check the smaller EPUB →