How does eBook conversion work—and what formats should you use?

Whether you’re shipping a novel, a handbook, or an image-heavy textbook, eBook conversion boils down to three things: clean structure, appropriate styling, and the right output format(s). Here’s a practical walkthrough

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The conversion workflow (what actually happens)

1. Assess the source
   • Start from the cleanest version you have (DOCX, Google Docs export, Markdown, or HTML).
   • Make styles semantic (use true Heading 1/2/3, lists, block quotes) instead of manual bold/size.
2. Decide layout type
   • Reflowable (most common): text flows to any screen size. Best for novels, nonfiction.
   • Fixed-layout: preserves page design/positioning. Use for children’s books, comics, design-heavy or equation-dense titles.
3. Normalize structure
   • One H1 for book title; H2 for chapters; avoid empty paragraphs and manual spacing.
   • Insert soft hyphens sparingly (or none), use proper em/en dashes, smart quotes.
   • Mark front/back matter (copyright, dedication, index).
4. Style with CSS (for EPUB)
   • Prefer simple, reader-friendly CSS; avoid device-specific hacks.
   • Use relative units (em, %) so text sizes scale.
5. Add metadata
   • Title, subtitle, author, series, language, publisher, ISBN.
   • Embed a high-quality cover image.
6. Build the eBook
   • Convert to EPUB first (the standard). From there, you can derive Kindle and other outputs.
   • Generate a logical TOC (NCX/nav), landmarks (start reading location), and page list if needed.
7. Validate & preview
   • Run epubcheck to catch spec issues.
   • Open on multiple previewers/devices (Kindle app/device, Apple Books, Kobo, Google Play Books, Android e-readers).
8. Distribute
   • Upload to stores (KDP for Amazon, Apple Books, Kobo, Google Play Books) or use an aggregator.
   • Note: stores usually apply their own DRM—don’t add your own unless required.

Which formats should you use?

The quick answer

• EPUB 3: your primary master format (universal across non-Amazon stores).
• Kindle (AZW/KFX): what Amazon delivers to readers. You typically upload EPUB or DOCX, and KDP converts it to Kindle formats.
• PDF: only when you must preserve exact layout (print replicas, workbooks). Not great for phones.
• DOCX: convenient upload source for retailers (KDP, Kobo Writing Life, etc.) if you don’t want to hand-craft EPUB.
• HTML/Markdown: great as intermediate formats for automated toolchains.

Platform cheat sheet

• Amazon Kindle (KDP): Upload EPUB or DOCX → Amazon serves AZW/KFX to users.
• Apple Books, Kobo, Google Play Books, Barnes & Noble: Upload EPUB (PDF optional for fixed-layout).

Choosing formats by use case (decision grid)

Use case	Recommended formats	Notes
General trade book (novel, memoir)	EPUB (master), upload to KDP as EPUB/DOCX	Reflowable, simple CSS
Nonfiction with images	EPUB; consider alt text; compress images	Keep images responsive; captions styled
Complex textbook/comic/children’s	Fixed-layout EPUB; PDF for print replica	Expect store-specific quirks
Corporate/manuals for download	EPUB + PDF	Give users a print and a reading version
Web-to-book pipelines	Markdown/HTML → EPUB	Automate with Pandoc/CI

Practical tips for a clean EPUB

• Images
  • Use reasonable resolution and compression; keep file size in check.
  • Prefer JPEG/WEBP for photos, PNG/SVG for line art and logos.
  • Set max-width: 100%; height: auto; in CSS so images scale.
• Fonts
  • System fonts are safest. If embedding, ensure you have a license and subset the font.
  • Provide fallbacks in CSS (e.g., font-family:
"YourFont", serif;).
• Navigation
  • Include a proper HTML5 nav table of contents and logical spine order.
  • Set a clear start page (usually first chapter).
• Accessibility
  • Add alt text to images.
  • Use correct heading hierarchy; avoid using bold as a fake heading.
  • Mark language (html lang="en"), and avoid conveying meaning with color alone.
• Footnotes & links
  • Use internal anchors for notes; ensure back-links return to the calling paragraph.
  • Keep external links fully qualified and check them.

Common pitfalls to avoid

• Overly complex page layouts in reflowable books (columns, floats, absolute positioning).
• Using tabs/spaces for indentation instead of CSS.
• Hard line breaks after every sentence (destroys reflow).
• Giant images and uncompressed media bloating the file.
• Missing or broken TOC, or no start reading location.
• Relying on desktop PDF for mobile reading (frustrating on phones).

Recommended tools (pick your lane)

No-code / low-code

• Vellum (Mac), Atticus, Kindle Create: friendly for authors; great for trade books.
• Pressbooks: WordPress-based, good for institutions and teams.

Pro / hands-on

• Calibre: convert/inspect; handy for quick checks.
• Sigil: visual EPUB editor with code view.
• Pandoc: powerful CLI for DOCX/Markdown/HTML → EPUB.
  • Example:

    pandoc manuscript.docx -o book.epub --toc --css=styles.css --metadata title="My Book"
    

• Adobe InDesign: export to EPUB/reflowable or fixed-layout; mind the export settings.

Validation & preview

• epubcheck: spec compliance.
• Kindle Previewer + Kindle apps/devices.
• Apple Books, Kobo Desktop, Google Play Books uploader preview.

Minimal CSS starter for reflowable EPUB

html, body { margin: 0; padding: 0; }
body { line-height: 1.5; widows: 2; orphans: 2; }
h1, h2, h3 { page-break-after: avoid; }
p { margin: 0 0 1em 0; }
img { max-width: 100%; height: auto; }
figure { margin: 1em 0; text-align: center; }
figcaption { font-size: 0.9em; opacity: 0.9; }

A short preflight checklist

• Headings are real headings; paragraphs aren’t manually spaced.
• Images compressed and scaled appropriately.
• nav TOC works; start location set.
• Metadata complete; cover embedded.
• Alt text present; links tested.
• Passed epubcheck; looks good on Kindle + at least one non-Kindle app.

Bottom line

• Make EPUB your master file. It’s the standard and converts well.
• Upload EPUB (or DOCX) to Amazon; let KDP generate Kindle formats.
• Use PDF only when you truly need print-exact layout.
• Keep structure semantic, CSS simple, images optimized, and always validate/preview.