What is ePub?
Definition: ePub (short for Electronic Publication) is an open standard file format specifically designed for eBooks and other digital publications, using the .epub file extension. It became an official standard of the International Digital Publishing Forum (IDPF), now part of W3C, in 2007, superseding the older Open eBook standard.
Structure: Technically, an ePub file is a ZIP archive. It bundles together web standard files like XHTML (for content structure), CSS (for styling and layout), images, fonts, and metadata (like title, author, publisher).
Key Characteristic: Its most significant feature is reflowability. This means the text automatically adjusts and reflows to fit the screen size and orientation of the device being used (e-reader, tablet, phone, computer), allowing for a comfortable reading experience without needing to constantly zoom or pan, unlike fixed-layout formats.
Key Features of ePub
- Reflowable Content: Adapts text display to fit various screen sizes and user font size preferences. Some ePubs can have fixed layouts (useful for comics or complex designs), but reflowable is the standard.
- Open Standard & Compatibility: As an open standard, ePub is supported by a vast range of e-readers (like Kobo, Nook), operating systems (iOS, Android, Windows, Mac), and software applications (like Apple Books, Google Play Books, Adobe Digital Editions, Calibre). While Amazon Kindle didn't natively support it for years, ePub files can now be read on Kindles via the "Send to Kindle" service.
- Multimedia & Interactivity: ePub 3 supports embedding multimedia elements like images, audio, and video, as well as interactive features (though compatibility and rendering can vary depending on the reading software/device).
- Accessibility: The format includes features designed for accessibility, such as logical reading order defined by structural markup (HTML5, ARIA roles), compatibility with screen readers and text-to-speech (TTS) technology, support for image descriptions (alt text), customizable text (size, font, spacing, color contrast), Media Overlays for synchronizing text and audio, and robust navigation structures (Table of Contents, page lists).
- Metadata: Can store detailed information about the book (title, author, publisher, language, ISBN).
- DRM Support: Can optionally include Digital Rights Management (DRM) to protect content from unauthorized copying or distribution.
- File Size: Often more lightweight than PDFs, especially for text-heavy books, saving storage space.
ePub vs. PDF
The primary difference lies in the layout:
| Feature |
ePub |
PDF |
| Layout |
Reflowable (adjusts to screen) |
Fixed (like a printed page) |
| Best For |
Reading on various screen sizes (phones, tablets, e-readers), text-heavy books |
Documents where exact layout/design is critical (print proofs, forms, graphic-heavy docs), universal viewing without special software |
| Readability |
High on most devices, customizable fonts/sizes |
Can be difficult on small screens (requires zoom/pan) |
| Interactivity |
Supports richer multimedia/interactivity (variable support) |
More limited interactivity |
| Editing |
Not designed for easy editing |
Requires specific software for editing |
| File Size |
Generally smaller for text |
Can be larger, especially with high-res images |
| Printing |
Not optimized for printing (layout changes) |
Optimized for printing (preserves layout) |
| Standard |
Open Standard (W3C) |
Open Standard (ISO / originally Adobe) |
Many library eBook platforms offer downloads in both formats, often recommending ePub for reading flexibility.
How to Open ePub Files
- iOS: Apple Books (built-in).
- Android: Google Play Books (built-in), numerous third-party apps (e.g., Lithium, Librera, Aldiko, Universal Book Reader).
- Windows/Mac: Calibre (popular free e-book manager), Adobe Digital Editions, Kobo app, Thorium Reader. Some web browsers also have extensions (like EPUBReader for Chrome).
- Dedicated E-readers: Most non-Kindle e-readers (Kobo, Nook, etc.) support ePub natively.
- Kindle: Use Amazon's "Send to Kindle" service (via email or app) to send the ePub file to your device; Amazon converts it for Kindle compatibility.
