Compress
Compress EPUB
Upload an EPUB to re-compress its internal files with maximum DEFLATE compression. The tool rebuilds the EPUB archive with optimized compression for HTML, CSS, XML, fonts, and images. View the before and after file sizes and download the compressed EPUB. The mimetype file is kept uncompressed as required by the EPUB specification.
Input formats
Output formats
Common uses
- Reduce an EPUB to meet a platform's file size limit
- Compress an EPUB before emailing or sharing
- Optimize an EPUB for faster delivery
Limitations
- Compression reduces ZIP overhead. Image quality is not changed in the default mode.
- The mimetype file must remain uncompressed per EPUB spec — this is handled automatically.
- DRM-protected EPUBs cannot be processed.
- For significant size reduction, the largest gains come from compressing large images inside the EPUB.
Your e-book files, handled privately
This tool runs entirely in your browser. Your files are never uploaded to a server. This tool does not remove DRM or bypass copyright protection. Only upload files you own or have permission to process.
Frequently asked questions
HTML, CSS, and XML files typically compress very well (40–70% reduction). Images in formats like JPG are already compressed and may see only small reductions. Large EPUBs with uncompressed assets see the biggest savings.
No. Re-compressing the archive does not change the reading content, formatting, or image quality. It only changes how files are stored inside the ZIP container.