Ebook formatting is not print formatting with different output. It’s a fundamentally different discipline. The sooner you understand that, the better your ebooks will look across every device, app, and platform your readers use.

In print, you control every aspect of the page: font, size, margins, line spacing, page breaks. The reader sees exactly what you designed. In ebooks, you control almost none of that. The reader controls font choice, font size, margins, and line spacing. Your formatting is a set of suggestions and structural rules that the reading device interprets.

This guide covers everything you need to know to produce professional ebooks: the underlying format, what you can and can’t control, platform-specific requirements, and the mistakes that break ebooks on readers’ devices.

Reflowable vs. fixed layout

Ebooks come in two fundamental types:

Reflowable layout

The text reflows to fit the reader’s screen size, font size, and margin preferences. This is the standard for fiction, nonfiction, memoir, and most text-based books. When a reader increases the font size on their Kindle, the text reformats to show fewer words per line and more pages. The content adapts.

Reflowable layout is what most authors need. It’s simpler to produce, works across all devices and screen sizes, and meets reader expectations.

Fixed layout

The pages have a fixed design — like a PDF. Each page looks exactly the same regardless of the device. Text doesn’t reflow. This is used for:

  • Children’s picture books
  • Comics and graphic novels
  • Heavily illustrated nonfiction (cookbooks, art books)
  • Books where text-image positioning is critical

Fixed layout ebooks are more complex to produce and have limitations: readers can’t change the font size, the reading experience is poor on small screens, and not all platforms support them equally.

For most authors reading this guide, reflowable layout is the right choice. The rest of this guide focuses on reflowable ebooks.

The EPUB format

EPUB (Electronic Publication) is the standard ebook format. It’s used by Apple Books, Kobo, Google Play Books, and most other ebook retailers. The current standard is EPUB 3, which supports:

  • HTML5 and CSS3 for content and styling
  • Embedded fonts
  • Audio and video (though rarely used in books)
  • Accessibility features (navigation, semantic markup, alt text)
  • Mathematical notation (MathML)

Amazon Kindle uses its own format (KPF/KFX), but Amazon’s publishing tools accept EPUB files and convert them. So in practice, a well-made EPUB works everywhere.

An EPUB file is essentially a ZIP archive containing:

  • XHTML files for each chapter (the actual content)
  • A CSS stylesheet that defines formatting
  • A navigation file (the table of contents)
  • A metadata file (title, author, publisher, ISBN, etc.)
  • Optionally: images, embedded fonts, and other media

You don’t need to build EPUBs by hand. Formatting tools generate them for you. But understanding the structure helps you troubleshoot problems and make better formatting decisions. Cambric generates standards-compliant EPUB 3 files with clean XHTML, properly structured navigation, and embedded metadata — all from the same project you use for your print PDF.

What you control (and what you don’t)

This is the most important concept in ebook formatting.

What you control

  • Document structure: Chapter divisions, headings, hierarchy
  • Table of contents: Which chapters and sections appear in navigation
  • Paragraph styles: Indentation (first-line indent or block style), spacing between paragraphs, alignment
  • Inline formatting: Bold, italic, small caps, superscript, subscript
  • Images: Size, placement, alt text
  • Scene breaks: Markers, ornaments
  • Front and back matter: What’s included and in what order
  • Default font suggestion: You can embed and suggest a font, but the reader can override it
  • Relative sizing: You can make headings larger than body text, but you can’t set exact point sizes

What you don’t control

  • Font choice: The reader picks their preferred font on most devices
  • Font size: The reader controls this entirely
  • Margins: Set by the reader and the device
  • Line spacing: Often adjustable by the reader
  • Page breaks within chapters: Text reflows, so “pages” are a device construct
  • Exact line length and hyphenation: Determined by device width and font size
  • Background color: Some readers use sepia or dark mode

This means your ebook formatting must be flexible and relative, not rigid and absolute. Specify that headings are 1.5em (1.5 times the body text size), not 18pt. Specify that images are 100% of the container width, not 600 pixels. Think in proportions, not fixed measurements.

Chapter navigation and table of contents

Every ebook needs a navigational table of contents (NCX in EPUB 2, nav document in EPUB 3). This isn’t the same as a visual “Contents” page in your front matter — it’s the structured navigation that appears when a reader taps the “Contents” or “Go To” button on their device.

Requirements:

  • Every chapter must have an entry. If Chapter 7 is missing from the navigation TOC, readers can’t jump to it.
  • Part and section entries are optional but helpful for books with complex structure.
  • Front matter entries (dedication, epigraph, introduction) are optional but recommended.
  • Back matter entries (acknowledgments, about the author, also-by) should be included.

Amazon specifically requires a navigational TOC and will reject or flag ebooks that don’t have one. Apple Books and Kobo strongly recommend it. There’s no reason to skip it.

In addition to the navigational TOC, you should include a visual Contents page in your front matter. This is the page the reader sees if they flip to the table of contents. It should list chapters (and parts, if applicable) as tappable links.

Image handling

Images in ebooks require different thinking than images in print.

Resolution and file size

Print images need 300 DPI. Ebook images do not. E-readers display images at screen resolution (typically 150-300 PPI for modern devices), and large images inflate your file size — which affects delivery costs on Amazon and download times for readers.

Optimize your images:

  • JPEG for photographs: Compress to 60-80% quality. Aim for under 256KB per image.
  • PNG for graphics, charts, and line art: Use PNG for images with text, sharp edges, or transparency.
  • Maximum dimensions: Amazon recommends images no larger than 1600 pixels on the longest side. Most devices display images well at 1000-1600 pixels wide.
  • Total file size: Amazon charges a delivery fee based on file size. Keep your total EPUB under 10MB if possible. Under 3MB is ideal for text-heavy books with few images.

Alt text

Every image should have descriptive alt text. This is an accessibility requirement — screen readers use alt text to describe images to visually impaired readers. It’s also a best practice that platforms increasingly check for.

Good alt text: alt="Map of the Kingdom of Aldoria showing the major cities and the route of the protagonist's journey"

Bad alt text: alt="map" or alt="image1.jpg" or no alt text at all.

Image placement

In reflowable ebooks, you have limited control over image placement. Images typically appear inline — they flow with the text, centered, at the width of the text container. You can’t wrap text around an image reliably in ebooks (some devices support it, many don’t).

For best results:

  • Place images between paragraphs, not in the middle of a paragraph
  • Center images
  • Include a caption below the image if needed
  • Don’t rely on exact positioning — the image will move based on the reader’s settings

CSS styling basics

Ebook formatting uses CSS (Cascading Style Sheets) to define how content looks. Even if you use a formatting tool that generates the CSS for you, understanding the basics helps you troubleshoot and customize.

Key CSS rules for ebooks:

/* Body text - use relative units */
body {
  font-family: Georgia, serif;
  line-height: 1.5;
  margin: 0;
  padding: 0;
}

/* First-line indent */
p {
  text-indent: 1.5em;
  margin: 0;
}

/* No indent after headings and scene breaks */
p.first, p.noindent {
  text-indent: 0;
}

/* Chapter headings */
h1 {
  font-size: 1.5em;
  text-align: center;
  margin-top: 3em;
  margin-bottom: 1em;
}

/* Scene break */
.scene-break {
  text-align: center;
  margin: 1.5em 0;
}

The critical principles:

  • Use em and % units, not px or pt. Relative units scale with the reader’s font size.
  • Don’t set absolute font sizes. font-size: 12pt will be ignored or overridden by most devices.
  • Don’t set page dimensions or margins. The device controls these.
  • Don’t use position: absolute or float for critical elements. These are unreliable in ebooks.

Common conversion mistakes

These are the errors that break ebooks. Most of them come from treating ebook formatting like print formatting.

Hard page breaks in the wrong places

A page break before every chapter heading is correct. A page break in the middle of a chapter (to push text to the next page for visual reasons) is not — in an ebook, there’s no “next page” in the print sense. The break creates an unexpected gap in the text.

Fixed font sizes

Setting body text to 12pt means it won’t respond to the reader’s font size controls. The text appears the same size regardless of settings, which is confusing and frustrating. Use relative units.

Non-embedded fonts

If you specify a font that isn’t embedded in the EPUB, the device falls back to its default font. Your carefully chosen typography vanishes. If you want a specific font, embed it — and make sure you have the license to do so.

Note: Many e-readers override embedded fonts anyway if the reader has selected their own font. Don’t rely on your font choice being preserved. Design your ebook so it looks good in Georgia, in the system sans-serif, and in whatever font the reader chooses.

Justified text assumptions

In print, justified text with good hyphenation looks clean. In ebooks, justification without hyphenation (and most e-readers have poor or no hyphenation) creates irregular spacing and “rivers” of white space, especially on small screens. Consider specifying left-aligned text, or accept that justified text won’t look as clean as it does in print.

Images with text baked in

If you have a chart or infographic with text as part of the image, that text can’t be scaled by the reader. On a phone screen, it may be unreadably small. Use HTML/CSS for text whenever possible, and keep image-based text to a minimum.

Tables

HTML tables in ebooks are problematic. They don’t reflow well on small screens and often extend beyond the screen edge. For simple tables, use HTML with percentage-based widths. For complex tables, consider converting them to images or restructuring the information as lists.

Testing on devices

Never publish an ebook without testing it on actual devices or emulators. What looks fine in your formatting tool may break on specific readers.

Amazon Kindle

  • Use Kindle Previewer (free desktop app from Amazon) to preview your ebook on simulated Kindle devices
  • Test on a physical Kindle if possible — the E Ink display renders differently than screens
  • Check: chapter navigation, images, scene breaks, front matter links

Apple Books

  • Preview in Apple Books on Mac or iOS
  • EPUB files can be opened directly in Apple Books for testing
  • Check: font rendering, image display, navigation

Kobo

  • Use Kobo Desktop or a physical Kobo device
  • Kobo’s EPUB rendering is generally good but has quirks with certain CSS properties

Google Play Books

  • Upload a test version to the Google Play Books partner center or open the EPUB in the Google Play Books app
  • Check: navigation, image rendering, metadata display

At minimum, test in Kindle Previewer and Apple Books. These two cover the vast majority of the ebook market. Cambric’s EPUB export passes EPUB Check validation automatically, which catches structural and accessibility issues before you begin device testing.

Platform-specific requirements

Amazon Kindle (KDP)

  • Accepts EPUB or DOCX files (Amazon converts to their format)
  • Requires a navigational table of contents
  • Cover image must be at least 1000 x 1600 pixels (2560 x 1600 recommended)
  • File size affects delivery cost (charged against royalties on the 70% royalty option)
  • Kindle supports a subset of CSS — avoid advanced CSS features

Apple Books

  • Accepts EPUB 3
  • Supports embedded fonts and advanced CSS
  • Requires ISBN for distribution (free ISBNs available through some distributors)
  • Generally the most standards-compliant platform

Kobo

  • Accepts EPUB
  • Supports most EPUB 3 features
  • Good CSS support
  • Distributed through Kobo Writing Life or aggregators

Google Play Books

  • Accepts EPUB or PDF (EPUB preferred)
  • Good EPUB 3 support
  • Requires a Google Play partner account

Draft2Digital, Smashwords, PublishDrive, etc.

Aggregator/distributor platforms accept EPUB and distribute to multiple retailers. They may apply their own validation and conversion. A clean, well-structured EPUB handles this smoothly. A messy one accumulates errors through each conversion step. Starting with a natively generated EPUB — rather than one converted from a print layout or Word document — gives you the cleanest foundation for multi-platform distribution.

The ebook is not a lesser product

Some authors treat ebook formatting as an afterthought — export the print interior as an EPUB and ship it. This produces ebooks with print artifacts: fixed margins that create tiny text on phones, page numbers in the text (meaningless in ebooks), running headers embedded in the content, and images sized for 300 DPI print.

Your ebook readers deserve a product designed for their device. That means:

  • Flexible, reflowable text
  • Properly structured navigation
  • Optimized images
  • Clean, semantic HTML
  • No print formatting artifacts

The ebook and print editions of your book should share the same content but have different formatting — each optimized for its medium.

For a deeper comparison of the two formats, see the EPUB vs. PDF guide. And for print-specific formatting, the KDP formatting guide covers that side of the equation.

Cambric generates print PDFs and EPUB ebooks from the same manuscript, with each output optimized for its medium. The print edition gets fixed pagination, running headers, and precise page layout. The ebook gets reflowable structure, navigational TOC, optimized images, and clean semantic markup. Same book, two formats, each done right. Cambric is a $109 one-time purchase desktop app with 20+ professional templates and Typst-based typesetting — your files stay on your machine, and you can use it for every book you publish. See how it compares to other formatting tools.