How to Create EPUB3 Files for Self-Publishing

Overview

EPUB3 is the current generation of the EPUB standard for reflowable ebooks. Retailers, libraries, and aggregators accept EPUB packages that combine HTML content, CSS styling, images, metadata, and machine-readable navigation into a single zip archive.

Authors rarely hand-code EPUB3 from scratch. Practical workflows import a structured manuscript into formatting software, apply a theme, preview reflow, and export a validated package. Understanding what is inside the package helps you fix validation errors and improve accessibility.

This guide explains EPUB3 structure, production habits, validation tools, and where desktop exporters such as Manusly fit relative to Word conversion and manual coding.

What EPUB3 is

EPUB3 builds on web standards: XHTML or HTML content documents, CSS for presentation, SVG for vector graphics, and JSON or XML navigation documents. Reading systems render EPUBs on phones, tablets, dedicated e-readers, and desktop apps.

Reflowable EPUBs adapt to user font size and screen width. Fixed-layout EPUBs preserve page geometry for picture books and some textbooks; they use a different profile within EPUB3.

Kindle uses proprietary formats internally but accepts EPUB upload for many titles, converting on ingestion. Clean EPUB3 still matters because conversion quality depends on semantic markup and valid packaging.

EPUB3 package structure

An EPUB file is a zip archive with extension .epub containing a mandatory mimetype file, META-INF/container.xml pointing to the package document, and an OEBPS or similar content folder.

The package document (often content.opf) lists manifest items, spine reading order, and metadata such as title, creator, language, and identifier. The spine order determines default linear reading sequence.

Navigation may use EPUB3 nav documents (HTML with nav elements) and legacy NCX for compatibility. Tables of contents should link to heading ids in chapter files.

Content documents

Each chapter is typically one XHTML file with headings, paragraphs, lists, and images referenced relatively. CSS may live in shared stylesheets referenced by multiple chapters.

Practical author workflow

Prepare the manuscript with consistent heading hierarchy. Chapter titles as level-one headings, scene sections as level-two if needed. Avoid text boxes and floating objects that do not map to HTML.

Import into a formatter that exports EPUB3 natively rather than saving Word as EPUB. Native exporters generate predictable markup and navigation.

Apply a theme or stylesheet designed for ebooks: comfortable line length via max-width rules, sensible heading spacing, and embedded fonts only where licensed.

Preview on phone and e-reader simulators. Change user font size in preview to confirm paragraphs reflow without overlap or clipped images.

Export, validate, fix source, repeat. Treat validation as part of writing release discipline, not an optional developer step.

Formatting rules that survive export

Use styles, not direct formatting. Bold applied as a character override without semantic meaning may survive visually but hurts accessibility and future theme changes.

Keep images inline with width constraints in CSS. Full-page images in reflowable books should use percentage widths rather than fixed pixel widths tied to print layout.

Avoid page-break CSS unless you understand retailer support. Forced breaks before chapters are common; forced breaks mid-paragraph are fragile on small screens.

Tables in ebooks need simplified structures. Complex merged cells from Word often break in EPUB. Consider splitting information into lists for narrow screens.

Metadata and navigation

Fill title, author, language, and identifier fields in your exporter. Language codes should match manuscript language for hyphenation and screen reader pronunciation.

Landmarks in nav documents mark cover, toc, body matter, and bibliography sections. They improve accessibility and some store quality checks.

Series metadata may live in OPF metadata and store dashboards. Keep spelling consistent across EPUB metadata and retailer forms.

Validation and testing

EPUBCheck is the reference validator maintained by the W3C publishing community. Run it on every export before wide distribution.

Calibre provides library viewing and conversion but should not be your only QA tool if you rely on its conversion to hide source errors.

Upload to KDP or other stores only after local preview passes. Store previewers add a second layer but should not be the first time you open the ebook.

Common mistakes

Exporting Word directly produces invalid nested spans, absolute positioning, and broken lists. Fix at source with a formatter import.

Missing or static TOCs frustrate readers on Kindle. Always generate linked navigation from headings.

Oversized image files inflate delivery cost and slow opening. Compress appropriately.

Font licensing violations embed commercial desktop fonts not licensed for ebook distribution. Use embeddable ebook fonts or reading-system defaults.

Mixing print page numbers into reflowable ebooks confuses readers when font size changes. Use logical navigation, not fixed page mimicry, unless you intentionally produce fixed layout.

Creating EPUB3 with Manusly

Manusly exports structured EPUB3 packages from desktop projects on Windows and macOS. Authors write or import manuscripts, apply themes, preview on simulated devices, and export EPUB3 alongside Kindle and print PDF when needed.

Manusly is appropriate when you want offline local projects and multi-format export without maintaining separate Word and InDesign files. It is not the only EPUB3 exporter; Calibre, Sigil, Pandoc, and other tools serve technical users with different tradeoffs.

Compare approaches in EPUB vs PDF and evaluate Manusly features against your accessibility and illustration requirements.

Kindle conversion notes

Amazon ingests EPUB for many titles and converts to Kindle formats internally. Conversion quality depends on clean HTML, valid CSS, and predictable image references.

Avoid JavaScript and interactive widgets unsupported on e-ink devices. Simple semantic markup survives conversion better than exotic CSS animations.

Kindle Previewer on desktop simulates post-conversion rendering. Use it after EPUB export when Kindle is a primary channel.

Separate Kindle-specific exports from generic EPUB when your formatter offers both. Subtle metadata and font subsetting choices may differ between targets.

Document which export target you validated last so wide-distribution uploads do not accidentally reuse a Kindle-only file with stripped navigation landmarks.

Related guides

• How to format a book for KDP
• Best book formatting software
• Fix Word to EPUB errors
• Self-publishing software overview