No ebook upload
The source, images, book metadata, and compressed result stay in current-tab memory.
EPUB Compressor
Compress EPUB files online by optimizing packaged images and rebuilding the ebook locally in your browser. Reduce EPUB size without uploading your book.
EPUB / LOCAL
Choose an EPUB file
Drop a DRM-free EPUB here or choose one from your device. The file stays in this browser tab.
The book is processed locally and is not uploaded for these tools.
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Compress EPUB files locally with an image-aware compressor
Reduce oversized JPEG, PNG, and WebP resources inside a DRM-free ebook. Select image quality and a maximum dimension; the browser keeps a replacement only when it is smaller, then rebuilds a separate EPUB. Text, metadata, navigation, fonts, SVG, GIF, audio, and video remain in the package. Results depend on the source, so the tool reports measured sizes rather than a promised percentage.
Smaller replacements only
A re-encoded image is discarded when it is not smaller than the original resource.
Original file preserved
The output ends in -compressed.epub; your existing ebook is never overwritten.
Core features
EPUB Compressor features and output
Use EPUB Compressor for the practical conversion task, with privacy and compatibility boundaries stated before download.
Practical EPUB image compression controls
Maximum dimension limits the longest image side to 3200, 2400, or 1600 pixels while preserving aspect ratio. Quality can be high, balanced, or smaller-file. Balanced at 2400 px is a sensible first test for many books. Use gentler settings for art, maps, diagrams, screenshots, and content readers may zoom. The browser never enlarges an image, and each candidate is compared by byte size before it can replace the original.
Conservative package handling
The compressor optimizes supported raster images declared in the manifest and applies ZIP deflate when rebuilding. It does not delete allegedly unused files, because CSS, SVG, media overlays, and reader-specific metadata can reference assets indirectly. Archive paths, entry counts, expansion ratios, large resources, and unsupported encryption are checked before work begins. This favors a complete book over an aggressively small but damaged package.
Results that reflect the actual ebook
A photo-heavy export with oversized images may shrink noticeably. A text novel, an already optimized EPUB, or a book dominated by fonts and media may barely change. PNG line art can also resist reduction. JPEG, WebP, audio, video, and fonts already use internal compression, so ZIP alone cannot transform them. The result reports original size, output size, and the number of images replaced, giving you evidence to decide whether the tradeoff is worthwhile.
Workflow
How to use EPUB Compressor in three steps
The file is processed by EPUB Compressor within the current browser tab.
Choose a DRM-free EPUB
The local parser checks the package and shows its title, version, chapter count, original size, and image count. A high image count suggests potential, but dimensions and prior encoding matter more.
Choose a compression profile
Start with balanced quality and 2400 px. Use higher settings for detailed artwork or lower settings only when size matters and you can inspect the result closely.
Download and compare
Open the new file in an EPUB reader and inspect the cover plus image-heavy chapters. Keep the original until the output works in representative reading systems.
Support boundary
EPUB Compressor compatibility and limits
Understand what EPUB Compressor preserves, changes, and does not support before processing.
Eligible images
JPEG · PNG · WebP
SVG and animated GIF are preserved to avoid damaging vectors or animation.
Quality hints
90% · 82% · 70%
Browser encoders can produce slightly different results; these are not universal visual scores.
Preserved assets
Text, CSS, fonts, SVG, media
Font subsetting, CSS pruning, media transcoding, and deletion of unknown assets are not performed.
Output
New local .epub
The tool does not remove DRM or guarantee a retailer, email, or device file-size limit.
FAQ
EPUB Compressor questions and answers
Direct answers about EPUB Compressor privacy, compatibility, and output.
How much smaller will my EPUB become?
It depends on the size and encoding of eligible images. An illustrated book can benefit; a text-led or previously optimized book may not. Use the measured result, not a generic reduction claim, and compare image quality before distribution.
Does compression change chapter text?
No. XHTML, metadata, reading order, and navigation are preserved. The selected controls target supported raster images. Readers can still render typography differently, but this process does not rasterize or intentionally rewrite selectable text.
Why did the file shrink only slightly?
The package may contain few eligible images, or its size may come from fonts, SVG, GIF, audio, and video that this conservative profile preserves. Images may also already be well optimized. A zero replacement count means no smaller raster candidate was found.
Can image quality decrease?
Yes. Lossy encoding and downscaling can remove detail. Maps, comics, screenshots, and fine labels deserve special care. Higher quality is safer; lower quality saves more. The tool prevents larger replacements, but only a person can judge whether a visual detail matters.
Will this meet a Kindle or Kobo size limit?
It may help, but platform limits and validation policies change. Check the current official requirements for your target, review the output, and validate the finished publication. This tool cannot certify acceptance by a retailer or transfer service.
Does it remove DRM or encrypted content?
No. Unsupported encryption is rejected and access controls are not bypassed. Standard font obfuscation resources are preserved rather than decoded. Use only files you own or are authorized to process.