Compress EPUB: Shrink Ebooks Without Uploading
Reduce EPUB file size by recompressing embedded images. See a live size estimate before you compress, and optionally convert images to grayscale for even smaller ebooks. Everything runs locally in your browser.
How to Compress an EPUB
Shrinking an ebook with img2img takes a few steps:
- Upload Your EPUB: Drag and drop a .epub file or click to browse
- Keep EPUB as Output: When the input is EPUB, the app switches to Compress mode
- Adjust Quality: Lower the quality slider to reduce image size inside the archive
- Optional Grayscale: Enable grayscale images to desaturate covers and figures for smaller files
- Check the Estimate: Review the predicted output size, then click Compress and download
What Gets Smaller
EPUB files are ZIP archives. Most of the bulk usually comes from images:
Image Re-encoding
JPEG, PNG, and WebP assets inside the book are re-encoded at your chosen quality. Text, CSS, and metadata stay intact.
Grayscale Mode
Convert embedded images to grayscale before encoding. Colorless images often compress better — useful for novels and scanned text.
Size Estimate
A heuristic estimate updates as you move the slider, then a sample encode refines the prediction so you know roughly how small the result will be.
Private & Local
Your ebook never leaves the device. No account, no upload limits, and no server-side storage.
Features
- ✓EPUB In, EPUB Out: Recompress images and keep a valid ebook package
- ✓Quality Slider: Trade visual fidelity for a smaller download
- ✓Grayscale Images: Optional desaturation for extra size savings
- ✓Output Size Estimate: Preview expected size before you commit
- ✓Browser-Only: Processing stays on your machine
Perfect for Amazon Kindle
A compressed EPUB is one of the best files you can send to a Kindle. Amazon Kindles read EPUB through Send to Kindle. Shrinking image-heavy books means faster transfers, more space on the device, and images that match e-ink screens. Grayscale compression is ideal for Paperwhite, Oasis, and Scribe — those displays are already black and white.
Why compressed EPUB is perfect for Kindle →