EPUB file size & duplicate image checker
Choose an .epub file. Every file inside is measured and fingerprinted in your browser, so you see exactly what to delete, merge or shrink before upload.
How it works
Ebooks grow quietly: an exported cover kept at 6000 px, the same logo saved as image1.png and image7.png, a full 12 MB CJK font for a few headings, images left over from a deleted chapter. A big file downloads slowly, and on Amazon KDP’s 70% royalty option the delivery fee is charged per megabyte, so every wasted MB costs on every sale.
How to use it: choose the .epub, adjust the limits if you like (images over 1000 KB or 3000 px on the longer side, fonts over 500 KB) and press Check size. The book is unzipped with the open-source JSZip library and each image, font and media file gets a SHA-1 fingerprint to find identical copies. Nothing is uploaded.
You get the file and unzipped size, a size breakdown by type, the 30 largest files with pixel sizes, and a fix list: problems (files not in the manifest, mimetype not first or compressed, BMP/TIFF images — all epubcheck or store failures) and checks (duplicate files with the MB wasted, files nothing points to, oversized images, large PNG photos, fonts to subset). Copy it as CSV, fix in Sigil, Calibre or your source files, then run epubcheck.
FAQ
Is my book uploaded?
No. The EPUB is opened in your browser only; nothing is sent or stored.
How does it know an image is unused?
It collects every href, src and CSS url() in the pages and stylesheets, plus the cover and navigation entries in the .opf. A manifest file nobody points to is listed as ‘check’ — a script or a reader-specific feature might still use it, so look before deleting.
Does it replace epubcheck?
No. It looks at size and packaging only, in plain words. Run epubcheck before KDP, Apple, Kobo or Google Play upload.
What is the free limit?
EPUB files up to 100 MB.