Convert EPUB3 to EPUB

Why Convert EPUB3 to EPUB?

Converting EPUB3 to EPUB (EPUB2) is essential when you need maximum compatibility across all e-reading devices and applications. While EPUB3 offers modern features like HTML5 and multimedia, some older e-readers, library lending systems, and reading applications only fully support the EPUB 2.0.1 specification.

Many e-book distribution platforms and digital libraries still process EPUB2 more reliably than EPUB3. If you are distributing e-books through multiple channels, converting to EPUB2 ensures your content renders correctly on every device, from modern tablets to older dedicated e-ink readers.

The conversion process downgrades HTML5 elements to XHTML 1.1, converts the navigation document to an NCX file, and simplifies CSS3 styling to CSS2. Content that relies on EPUB3-specific features like JavaScript interactivity, MathML, or embedded audio/video is converted to static equivalents or fallback content.

For text-focused books like novels, non-fiction, and simple technical documents, the downgrade from EPUB3 to EPUB2 preserves virtually all content with minimal loss. The primary differences are in advanced layout features and multimedia capabilities, which are typically not essential for standard reading experiences.

Key Benefits of Converting EPUB3 to EPUB:

• Universal Compatibility: Works on all e-readers, including older models
• Library Systems: Compatible with all digital lending platforms
• Reliable Rendering: Consistent display across all devices
• Smaller Files: Simplified structure produces more compact files
• Distribution Ready: Accepted by all e-book stores and platforms
• Proven Format: Decades of reliable e-reader support
• Simple Structure: Easier to validate and troubleshoot

Practical Examples

Example 1: Navigation Conversion

Input EPUB3 navigation (nav.xhtml):

<nav epub:type="toc">
  <h1>Table of Contents</h1>
  <ol>
    <li><a href="ch01.xhtml">Chapter 1</a></li>
    <li><a href="ch02.xhtml">Chapter 2</a>
      <ol>
        <li><a href="ch02.xhtml#s1">
          Section 2.1</a></li>
      </ol>
    </li>
  </ol>
</nav>

Output EPUB2 navigation (toc.ncx):

<ncx xmlns="http://www.daisy.org/z3986/...">
  <navMap>
    <navPoint id="ch01" playOrder="1">
      <navLabel><text>Chapter 1</text></navLabel>
      <content src="ch01.xhtml"/>
    </navPoint>
    <navPoint id="ch02" playOrder="2">
      <navLabel><text>Chapter 2</text></navLabel>
      <content src="ch02.xhtml"/>
      <navPoint id="s1" playOrder="3">
        <navLabel><text>Section 2.1</text></navLabel>
        <content src="ch02.xhtml#s1"/>
      </navPoint>
    </navPoint>
  </navMap>
</ncx>

Example 2: HTML5 to XHTML Downgrade

Input EPUB3 content (chapter.xhtml):

<section epub:type="chapter">
  <h1>Modern Web Design</h1>
  <aside epub:type="sidebar">
    <p>Tip: Use responsive layouts.</p>
  </aside>
  <figure>
    <img src="layout.png" alt="Layout"/>
    <figcaption>Figure 1</figcaption>
  </figure>
</section>

Output EPUB2 content (chapter.xhtml):

<div class="chapter">
  <h1>Modern Web Design</h1>
  <div class="sidebar">
    <p>Tip: Use responsive layouts.</p>
  </div>
  <div class="figure">
    <img src="layout.png" alt="Layout"/>
    <p class="caption">Figure 1</p>
  </div>
</div>
(Valid XHTML 1.1 with CSS2 styling)

Example 3: Metadata Conversion

Input EPUB3 package (content.opf):

<package version="3.0">
  <metadata>
    <dc:title>My Book</dc:title>
    <dc:creator>Author Name</dc:creator>
    <dc:language>en</dc:language>
    <meta property="dcterms:modified">
      2024-01-15T00:00:00Z</meta>
    <meta property="schema:accessMode">
      textual</meta>
  </metadata>
</package>

Output EPUB2 package (content.opf):

<package version="2.0">
  <metadata
    xmlns:dc="http://purl.org/dc/elements/1.1/"
    xmlns:opf="http://www.idpf.org/2007/opf">
    <dc:title>My Book</dc:title>
    <dc:creator opf:role="aut">
      Author Name</dc:creator>
    <dc:language>en</dc:language>
    <dc:date>2024-01-15</dc:date>
  </metadata>
</package>

Frequently Asked Questions (FAQ)

Q: What is the difference between EPUB3 and EPUB2?

A: EPUB3 uses HTML5 and CSS3 with support for multimedia, JavaScript, MathML, and SVG, while EPUB2 uses XHTML 1.1 and CSS2 with simpler content capabilities. EPUB3 uses a navigation document (nav.xhtml), while EPUB2 uses an NCX file for table of contents. EPUB3 is maintained by the W3C, while EPUB2 was the final version from IDPF.

Q: Will I lose content during conversion?

A: For text-based books, virtually no content is lost. Text, headings, lists, tables, images, and basic formatting are fully preserved. Features that rely on EPUB3-specific capabilities (JavaScript interactivity, embedded audio/video, MathML, CSS3 animations) may be converted to static fallbacks or simplified representations.

Q: Do both formats use the .epub extension?

A: Yes, both EPUB3 and EPUB2 files use the .epub file extension. The version is determined by the content inside, specifically the version attribute in the OPF package file. E-reading software detects the version automatically and renders the content accordingly.

Q: Which e-readers need EPUB2?

A: Older e-ink readers from before 2013 may have limited EPUB3 support. Some older Kobo, Nook, and Sony Reader models work better with EPUB2. Additionally, some digital library systems and distribution platforms process EPUB2 more reliably. Modern readers like Apple Books, Kobo (newer models), and Calibre support both versions.

Q: What happens to CSS3 styling?

A: CSS3 properties are downgraded to CSS2 equivalents where possible. Features like flexbox, grid, custom properties, and CSS3 transforms are removed or replaced with simpler layout approaches. Basic properties like fonts, colors, margins, and borders are preserved as they are supported in CSS2.

Q: Are fixed-layout EPUB3 books supported?

A: Fixed-layout is an EPUB3 feature that does not exist in EPUB2. Fixed-layout EPUB3 books are converted to reflowable EPUB2 with the content restructured for text flow. For books that depend heavily on fixed positioning (comics, children's books), significant layout changes may occur.

Q: How is the table of contents converted?

A: EPUB3's navigation document (nav.xhtml using HTML5 nav element) is converted to EPUB2's NCX (Navigation Center eXtended) format. The hierarchical structure is preserved, with navigation points maintaining their nesting and reading order. Both formats support multi-level table of contents.

Q: Can I validate the converted EPUB2?

A: Yes, the converted EPUB2 can be validated using EPUBCheck, the official EPUB validation tool. EPUBCheck verifies that the file structure, metadata, content documents, and navigation conform to the EPUB 2.0.1 specification. You can also use Sigil's built-in validation for quick checks.