What is a .epub file?
Electronic Publication · eBook · International Digital Publishing Forum · 2007
EPUB is the open standard for eBooks. It is a zipped package of HTML and images whose text reflows to fit any screen, so a book reads comfortably on a phone, tablet or e-reader without pinching and zooming.
What is a .epub file used for?
An EPUB is essentially a small website in a zip: HTML chapters, styles and images, plus a table of contents. Reading apps render it and let the text reflow to any screen size and font.
That reflowable design is what separates an eBook from a fixed-layout PDF. Change the font size and the pages simply re-flow.
It is supported by most e-readers and apps. The notable exception is the Kindle, which historically used its own formats, though newer Kindles now accept EPUB.
What opens a .epub file?
The .epub format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Calibre
- Edge
- Thorium Reader
macOS
- Apple Books
- Calibre
- Thorium Reader
Linux
- Calibre
- Foliate
Web
- Some browser reader extensions
Open a .epub file step by step
- Confirm the file really is a .epub. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Calibre or Edge.
- On Mac, use Apple Books or Calibre.
- On Linux, try Calibre or Foliate.
- Still stuck? Convert the .epub to PDF, which opens more widely.
Why can't I open my .epub file?
Almost always because no installed app understands EPUB. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .epub at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .epub file
You can convert a .epub file to PDF, MOBI, AZW3.
Calibre converts EPUB to PDF, MOBI or AZW3 and is the tool the format's own community uses. A PDF export freezes the layout at one page size, which is exactly what EPUB's reflowable text exists to avoid.
What is the .epub file signature (magic bytes)?
A .epub file starts with the hex bytes 50 4B 03 04, which read as PK.. in ASCII. Programs identify EPUB by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for EPUB. For a full breakdown, see the ZIP file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 50 4B 03 04 | 0 | PK.. | ZIP header; mimetype file follows |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .epub file?
EPUB is the open standard for eBooks. It is a zipped package of HTML and images whose text reflows to fit any screen, so a book reads comfortably on a phone, tablet or e-reader without pinching and zooming.
How do I read an EPUB on a Kindle?
Newer Kindles accept EPUB via Send to Kindle. For older ones, convert the EPUB to MOBI or AZW3 with Calibre.
Comparisons
Related formats
Sources
Details on this page were checked against authoritative references. How sources are ranked and what is deliberately left out is set out in the methodology.