EPUB file format: what it is and how to use it
EPUB is the open e-book standard: a ZIP of HTML, CSS and metadata that reflows to any screen, readable on every device that is not a pre-2022 Kindle. Learn when to use it and what to choose instead.
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What is a EPUB file?
An .epub file is an e-book in EPUB, the open standard maintained by the W3C/IDPF: a ZIP package containing XHTML chapters, CSS styles, images and an OPF manifest with metadata, spine order and navigation. Text reflows to the reader's screen, font and margins; fixed-layout variants exist for comics and children's books. It is the format every non-Amazon e-reader and store is built around.
When should you use EPUB?
- Publishing e-books: the accepted format of Kobo, Apple Books, Google Play and libraries.
- Reflowable reading: users control font, size and spacing, with accessibility built in.
- Now even on Kindle: Amazon's Send-to-Kindle accepts EPUB and converts it.
When is another format a better fit?
For print-replica documents use PDF. For ancient Kindle devices MOBI was the container, now superseded even at Amazon. For structured, annotated reading inside apps, the web stack itself (HTML) sometimes beats a packaged book.
The short version: EPUB is the e-book standard: publish in it, read on everything, and let Kindle ingest it too.
How to open a EPUB file
On Windows
Double-click the file, or open it with Calibre.
On macOS
Apple Books opens EPUB files on macOS.
In your browser
Open EPUB files right in a browser tab or with the dexrr viewer. No install, no upload.
Also opens in
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Apple Books -
Calibre -
Thorium Reader -
Google Play Books
View or convert EPUB files
A quick preview or a new format. No install, no upload.
EPUB technical details
- Full name
- EPUB e-book
- Extensions
- .epub
- MIME type
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application/epub+zip - Magic bytes
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50 4B 03 04 (ZIP container) - Compression
- Lossless
- Developer
- IDPF / W3C
- Specification
- www.w3.org
EPUB questions, answered
How do I open an .epub file?
Apple Books, Kobo, Google Play Books, Calibre and most reader apps open it; browsers need an extension or web reader. dexrr displays and converts epub files in your browser.
Can I convert EPUB files online?
Yes, dexrr converts epub locally in your browser: EPUB to PDF for printing or EPUB to MOBI for legacy Kindles.
Is EPUB better than MOBI?
Yes on every axis except ancient-Kindle compatibility: richer layout, open standard, and now accepted by Amazon itself. MOBI is the legacy sibling.
Why won't my Kindle read .epub directly?
Older Kindles spoke only Mobipocket-derived formats. Send the EPUB via Send-to-Kindle or convert to MOBI/AZW3 for direct sideloading.
Is the EPUB format outdated?
No, EPUB 3 is the current global e-book standard, maintained by the W3C and adopted by every major platform outside legacy Kindle.