Compress EPUB ebooks without breaking them
An EPUB is a ZIP archive of web pages, stylesheets, images, and fonts. The text is tiny: a whole novel is usually under a megabyte. When an EPUB is large, the cause is almost always images, like a cover saved at print resolution, photos stored as PNG, or illustrations far bigger than any screen. Embedded fonts are the next biggest cause. This tool shrinks those, removes junk files, and rebuilds a valid EPUB that opens in Apple Books, Kobo, Google Play Books, Calibre, and other reading apps.
Everything happens in your browser. Your books are never uploaded.
How to use it
- Choose one or more
.epubfiles, or drag them onto the box. - Pick the largest image size and photo quality. The recommended settings look sharp on phones, tablets, and e-ink readers.
- Check each result: savings, the verification badge, and what happened to every image.
- Download the compressed ebook, or all of them at once as a ZIP.
Why EPUB files get too big
| Cause | What the tool does |
|---|---|
| Images larger than any reading screen | Resizes them to the size you choose and re-saves photos as JPEG. Even large tablets display about 2048 pixels. |
| Photos stored as PNG or BMP | Converts them to JPEG and updates every reference in the book: the package file, chapters, stylesheets, and table of contents. |
| Embedded fonts | Optionally removes them, along with the stylesheet rules that load them |
| Uncompressed text | Some tools store chapters without compression. All text is re-compressed. |
| Junk from the build process | Removes files like .DS_Store and __MACOSX that aren't part of the book |
Transparent images, diagrams, and images of text stay as PNG so they stay sharp. Phone photos keep their rotation, and an image is only replaced when the new version is meaningfully smaller.
How each book is checked
After compressing, the tool reopens its own output and checks it the way a reading system would. The mimetype file must be first and uncompressed, as the EPUB standard requires. The package file must be found, every file in the manifest must exist, every chapter in the reading order must be present, and every image, stylesheet, and link referenced from the chapters must resolve. Every checksum must also match. Problems that were already in the original aren't blamed on the compression. The green Verified badge means everything passed. In testing, compressed books opened in pandoc with exactly the same text as the originals.
Will it work with Kindle?
Kindle apps and devices accept EPUB files sent through Send to Kindle. Amazon's email limit is 50 MB, so compressing a large illustrated EPUB is often what makes it send at all. For books you publish through Kindle Direct Publishing, Amazon recommends a cover of 1600 by 2560 pixels, which is why the cover is kept at full size by default.
Frequently asked questions
Will my ebook look different?
Text, layout, styles, and links are untouched. Images are resized and re-saved at a quality that looks the same on screen. Removing fonts is optional and off by default, and it's the only option that changes how the book looks.
Are my books uploaded?
No. The EPUB is opened, optimized, and rebuilt inside your browser.
Can it compress DRM-protected EPUBs?
No. Books with DRM from a store are encrypted, and changing them isn't possible or permitted. The tool detects them and leaves them alone. Font obfuscation, which many publishers use only to protect embedded fonts, isn't DRM and works fine.
Does it compress the text?
The text is re-compressed inside the EPUB, which helps when a tool stored it uncompressed. Chapter files themselves aren't minified, because ebook reading systems treat spacing in HTML like web browsers do, and removing it could join words together.
How small will my book get?
Illustrated books, cookbooks, and photo books often shrink 50 to 90 percent. Text-only novels are already small and may change very little, unless they embed several fonts.