What is a .epub file? (EPUB)

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.

How to open 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. For a step-by-step walkthrough, see how to open a .epub file.

Windows

Calibre
Edge
Thorium Reader

macOS

Apple Books
Calibre
Thorium Reader

Linux

Calibre
Foliate

Web

Some browser reader extensions

How to convert a .epub file

You can convert a .epub file to PDF, MOBI, AZW3 using a conversion tool or the export menu of an app that opens it.

.epub file signature (magic bytes)

Programs recognise a .epub file by the bytes at the start of the file, not by its name. These are the signatures for EPUB. For a full breakdown, see the EPUB file signature page.

Hex signature	Offset	Note
50 4B 03 04	0	ZIP header; mimetype file follows

See the full magic-numbers reference for every format.

Frequently asked questions