EPUB 3 vs EPUB 2, KEPUB, and Fixed-Layout: A Decision Guide for Indie Authors

Choosing an ebook format feels like a technical decision, but it is really a publishing decision. The format you pick affects where your book can be sold, how it looks on different devices, and how much time you spend fixing problems. This guide walks through EPUB 3, EPUB 2, KEPUB, and fixed-layout EPUB so you can choose with confidence.

Start with the reader experience you need

Before comparing formats, decide what kind of reading experience your book requires. Most novels, memoirs, and nonfiction books are reflowable: text wraps to fit the screen, and readers control font size and margins. Reflowable EPUB is the default for good reason—it works on phones, tablets, and dedicated e-readers without custom design work.

Some books need a fixed layout: children's picture books, comics, cookbooks with complex spreads, or any title where text and images must stay in exact positions. Fixed-layout EPUB preserves page geometry but limits reader control and can be harder to sell across stores.

Ask yourself: if a reader changes the font size, does the book still make sense? If yes, you want reflowable. If no, you may need fixed layout.

EPUB 3: the modern standard

EPUB 3 is the current specification maintained by the W3C. It supports HTML5 and CSS3, embedded fonts, media overlays (read-aloud), MathML, and better accessibility features. For most authors, EPUB 3 is the right starting point.

Key advantages:

Works on all major retailers that accept EPUB, though some convert it internally.
Supports semantic markup like epub:type for accessibility and navigation.
Allows fallbacks for older reading systems.
Future-proof: EPUB 2 is deprecated and will not receive updates.

However, EPUB 3 is not a magic bullet. Some older devices and apps still render EPUB 3 poorly, especially if you rely on advanced CSS. The practical approach is to build a clean EPUB 3 file with simple, robust styling, then test it on your target devices.

EPUB 2: still relevant?

EPUB 2 was the standard for years and is still accepted by many retailers. It uses XHTML 1.1 and CSS 2.1, with limited support for HTML5. If you are producing a simple novel and want maximum compatibility with very old devices, EPUB 2 can work.

But EPUB 2 has real limitations:

No native support for audio, video, or MathML.
Weaker accessibility features.
No semantic inflection for assistive technologies.
Retailers are gradually dropping support or converting EPUB 2 to EPUB 3 internally.

If you already have an EPUB 2 file that validates and looks good, you do not need to panic. But for new projects, EPUB 3 is the better investment.

KEPUB: Amazon's internal format

KEPUB is a Kindle-specific format used by Amazon. It is essentially EPUB with Amazon's proprietary extensions, and it is not something you typically create by hand. When you upload a reflowable EPUB or DOCX to Amazon KDP, Amazon converts it to KEPUB for delivery to Kindle devices and apps.

Why does this matter? Because Amazon's conversion can change your formatting. Lists, tables, and complex CSS may render differently after conversion. To minimize surprises:

Keep your EPUB simple and semantic.
Avoid absolute positioning and fixed dimensions in reflowable books.
Use page-break-before: always sparingly; Amazon may handle it differently.
Test the converted book using Kindle Previewer or the Look Inside feature after publishing.

You do not need to produce a KEPUB file yourself. Focus on a clean EPUB 3, and let Amazon handle the conversion. Always check Amazon's current formatting guidelines because requirements change.

Fixed-layout EPUB: when and how

Fixed-layout EPUB is a specialized form of EPUB 3 where each page is a fixed-size XHTML document. It is used for children's books, comics, and highly designed layouts. Apple Books, Kobo, and Amazon (via KDP) support fixed-layout EPUB, but each has its own quirks and submission rules.

Fixed-layout is harder to produce because:

You must design for specific screen sizes or use scalable vector graphics.
Text may not be selectable or searchable unless you add hidden text layers.
Accessibility is more difficult; you need to provide alternative text and reading order.
File size can balloon if images are not optimized.

If your book is a novel, fixed-layout is almost always the wrong choice. If you have a picture book, consider whether a reflowable layout with images set to max-width: 100% might be acceptable. Sometimes it is; sometimes it is not.

Step-by-step: choose your format

Use this checklist to make a decision:

Identify your book type. Is it text-heavy, image-heavy, or interactive? Text-heavy books should be reflowable EPUB 3. Image-heavy books may need fixed layout.
List your target retailers. Write down every store where you plan to sell. Check each store's current format requirements in their official help documentation. Do not rely on blog posts from 2018.
Check device support. If you expect readers on very old e-readers, test a sample EPUB 3 on those devices. If it fails, consider providing an EPUB 2 fallback.
Decide on KEPUB. If you are selling on Amazon, you will not upload KEPUB directly. Upload a clean EPUB or DOCX and let Amazon convert. Verify the result with Kindle Previewer.
Evaluate fixed-layout need. If your book requires precise positioning, plan for fixed-layout EPUB 3. Otherwise, avoid it.
Validate your file. Use EPUBCheck to catch errors. Fix all errors before uploading. Warnings are usually safe to ignore, but review them.
Test on real devices. Open your EPUB in Apple Books, Google Play Books, Kobo, and Kindle Previewer. Check navigation, font resizing, and image display.

Worked example: converting a novel

Suppose you have a 80,000-word novel with no images. You want to sell on Amazon, Apple Books, Kobo, and Google Play. Your best choice is a reflowable EPUB 3 file.

Steps:

Export your manuscript from your writing tool as DOCX or HTML.
Use a conversion tool to produce EPUB 3. If you use EpubBit, you can convert DOCX to EPUB and then run validation checks.
Run EPUBCheck. Fix any errors. Common errors include missing dc:title or incorrect toc.ncx.
Open the EPUB in a reader. Change the font size. Does the text reflow correctly? Are chapter headings consistent?
Upload the EPUB to each retailer. For Amazon, upload the EPUB or DOCX; Amazon will convert to KEPUB.
After publishing, download a sample from each store and inspect it. If formatting is broken, fix the source EPUB and re-upload.

This process works for most fiction and narrative nonfiction. The key is to keep your EPUB simple and validate it.

Common pitfalls and how to avoid them

Even experienced authors run into format issues. Here are the most common ones:

Using fixed layout for a reflowable book. This breaks font resizing and can make your book unreadable on phones. Only use fixed layout when absolutely necessary.
Ignoring accessibility. EPUB 3 supports accessibility features like epub:type="noteref" and alt text. Adding them improves the reading experience for everyone and may be required by some retailers.
Forgetting to test on Kobo. Kobo's reading app sometimes handles CSS differently. Test your EPUB on a Kobo device or app.
Overlooking metadata. Your EPUB's metadata (title, author, language, identifier) must be correct. Errors can cause your book to be listed incorrectly or rejected.
Assuming Amazon's conversion is perfect. It is not. Always preview your converted book.

Where EpubBit fits in your workflow

EpubBit is designed to help you produce and validate EPUB files without needing to learn command-line tools. You can use it to convert your manuscript, check for common errors, and preview how your book will look. It is not a replacement for testing on real devices, but it can catch many issues early.

For example, after converting your DOCX to EPUB 3, you can run EpubBit's validation to see if your file meets the EPUB 3 specification. Then you can fix metadata or structural issues before uploading to retailers. This saves time and reduces the chance of rejection.

Conclusion

For most indie authors, the answer is straightforward: produce a clean, validated EPUB 3 file with reflowable text. Upload it to retailers, and let Amazon convert it to KEPUB. Use fixed-layout EPUB only when your content truly requires it. EPUB 2 is legacy; only use it if you have a specific compatibility need.

Always verify current retailer requirements in their official documentation, because formats and policies change. Test your book on the devices your readers actually use. With a simple, validated EPUB 3, you will spend less time troubleshooting and more time writing your next book.