How much can I reduce my EPUB file size?

There is no fixed saving. This page can optimize JPEG and opaque PNG images in your browser, up to 200 entries; transparent PNGs keep their format. The server repacks the ZIP and can remove unused assets. A book that is already compressed may not get smaller. Compare the returned file size with the original.

Does compression affect ebook quality?

Image resizing and JPEG re-encoding are lossy. Turn off Optimize images to keep the image bytes unchanged. Removing unused assets changes the package manifest. Keep your original and preview the returned book in your reader before replacing it.

What compression levels are available?

Three, and they are Deflate effort levels, not image settings: Low is Deflate 3 (fastest, largest), Medium is 6 (the default), Maximum is 9 (slowest, smallest). They apply to the compressible entries — text, XHTML, CSS, OPF. Images, fonts and other already-compressed entries are stored as-is at every level, so moving from Low to Maximum never changes how a picture looks. Picture size is the separate "Optimize images" controls above.

Will compressed EPUB still work on Kindle, Kobo, and Apple Books?

The tool repacks the EPUB format rather than converting it to a different book format. Compatibility still depends on the source book and each reader or store. Validate the result, preview it on the device you use, and check the current requirements of the service you upload to.

Why is my EPUB file so large in the first place?

Check the archive entries to see which assets take space. Images, embedded fonts, media and unused files can all contribute. The compression guide at /compress-large-epub explains how to inspect and optimize a copy without guessing from the page count.

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Compress EPUB Files

Compress EPUB files for Kindle, Kobo, and KDP limits. Free online compressor — strips unused assets, repacks the ZIP, optional in-browser image optimization.

Select EPUB files

or drop EPUBs here

Frequently asked questions

How much can I reduce my EPUB file size?: There is no fixed saving. This page can optimize JPEG and opaque PNG images in your browser, up to 200 entries; transparent PNGs keep their format. The server repacks the ZIP and can remove unused assets. A book that is already compressed may not get smaller. Compare the returned file size with the original.
Does compression affect ebook quality?: Image resizing and JPEG re-encoding are lossy. Turn off Optimize images to keep the image bytes unchanged. Removing unused assets changes the package manifest. Keep your original and preview the returned book in your reader before replacing it.
What compression levels are available?: Three, and they are Deflate effort levels, not image settings: Low is Deflate 3 (fastest, largest), Medium is 6 (the default), Maximum is 9 (slowest, smallest). They apply to the compressible entries — text, XHTML, CSS, OPF. Images, fonts and other already-compressed entries are stored as-is at every level, so moving from Low to Maximum never changes how a picture looks. Picture size is the separate "Optimize images" controls above.
Will compressed EPUB still work on Kindle, Kobo, and Apple Books?: The tool repacks the EPUB format rather than converting it to a different book format. Compatibility still depends on the source book and each reader or store. Validate the result, preview it on the device you use, and check the current requirements of the service you upload to.
Why is my EPUB file so large in the first place?: Check the archive entries to see which assets take space. Images, embedded fonts, media and unused files can all contribute. The compression guide at /compress-large-epub explains how to inspect and optimize a copy without guessing from the page count.

What "compress EPUB" actually means

An EPUB is a ZIP archive containing chapters, stylesheets, fonts, images and metadata. This browser tool can resize and re-encode supported images before upload, then the server repacks the archive and optionally removes unused assets. Image optimization is lossy: check small text, diagrams and transparent artwork before accepting the result. Removing assets can also change the package manifest. Keep the original and preview the returned book in your reader. See the EPUB compression guide for the workflow and the limits.

How much can you compress an EPUB?

Inspect the archive to find the largest entries. Uncompressed text can shrink when repacked with Deflate, while text already compressed efficiently may change little. Large images can also shrink through the optional browser resize and re-encode, at a quality cost. Unused assets can be removed when the scanner can determine they are unreferenced. Compare the resulting bytes rather than expecting a fixed reduction. The reader guide can help you choose where to preview the result.

Kindle, Kobo, and KDP upload limits

Upload limits and delivery charges depend on the store, account and submission method. Check the store's current published requirements before choosing a size target; there is no universal EPUB size that guarantees acceptance or a particular royalty. Inspect which assets take space, optimize a copy, and validate and preview it after repacking. The KDP upload guide and Send to Kindle guide distinguish publishing from sending a personal document.