What Is an EPUB File? The Complete Guide to the EPUB Format
EPUB is the standard file format for ebooks. It works on Kobo, Apple Books, Kindle (since 2022), Google Play Books, and reading apps on every platform. Here's what EPUB files are, how they work, and what you can do with them.
EPUB in one sentence
An EPUB file is a ZIP archive containing HTML5 pages, images, fonts, and metadata — like a mini website packaged as a single file that any EPUB reader can open and reflow to fit any screen size.
What does EPUB stand for?
EPUB stands for Electronic PUBlication. It's an open standard maintained by the W3C (World Wide Web Consortium), formerly by the IDPF (International Digital Publishing Forum). The current version is EPUB 3.3, published in 2023.
How EPUB differs from PDF
| EPUB | ||
|---|---|---|
| Text layout | Reflowable — adapts to screen | Fixed — like a printed page |
| Font size | User-adjustable | Fixed (zoom only) |
| Dark mode | Native support | Limited |
| Navigation | Chapter TOC, page landmarks | Page numbers only |
| Accessibility | Full screen reader support | Often poor |
| Best for | Books, articles, long-form reading | Documents with exact layout (forms, brochures) |
What's inside an EPUB file?
An EPUB is a ZIP file. If you rename book.epub to book.zip and extract it, you'll find:
- XHTML/HTML5 files — one per chapter, containing the actual text
- CSS files — typography and layout styles
- Images — cover art and inline images
- content.opf — the manifest: lists all files and metadata (title, author, language, publication date)
- toc.ncx / nav.xhtml — the table of contents for navigation
- mimetype — a plain text file declaring
application/epub+zip
EPUB 2 vs EPUB 3
EPUB 2 (2010) used XHTML and a separate NCX navigation file. EPUB 3 (2011, current) uses HTML5, adds MathML for equations, audio/video, ARIA accessibility attributes, and a unified navigation document. Most modern readers support EPUB 3. Full EPUB 3 vs EPUB 2 comparison →
Where do you get EPUB files?
- Bookshops: Kobo, Apple Books, Google Play Books, Smashwords, and most independent ebook retailers sell DRM-free or Adobe DRM EPUBs
- Libraries: OverDrive/Libby and Hoopla let you borrow EPUBs for free with a library card. How to borrow EPUBs from your library →
- Project Gutenberg: 70,000+ public domain books as free DRM-free EPUBs
- Standard Ebooks: high-quality formatted versions of public domain texts
- Convert from PDF: if you have PDFs (academic papers, reports, books), convert them to EPUB for a better reading experience
How to open an EPUB file
See the complete guide to opening EPUBs on every device →
Quick summary:
- Mac: double-click → Apple Books opens it automatically
- Windows: drag into Microsoft Edge, or install Thorium Reader
- iPhone/iPad: tap the file → "Open in Books"
- Android: open with Google Play Books or Moon+ Reader
- Kindle: send via Send to Kindle
- Kobo: USB transfer or Kobo desktop app
Converting PDF to EPUB
If you have PDFs you want to read as EPUBs — academic papers, books, reports — you can convert them in about 30 seconds. The converter extracts text in reading order, runs OCR on scanned pages, and preserves tables as HTML.
Convert a PDF to EPUB — free, no account, works in your browser.
Convert PDF to EPUB →