EPUB Formatting: Reflowable vs Fixed Layout, and How to Pass Store Validation
When your ebook should reflow and when it must not, why Kindle now takes EPUB, and what EPUBCheck validation catches before Apple, Kobo and Google do.
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EPUB is the universal ebook format: one file works on Kindle, Kobo, Apple Books, Google Play and virtually every reader app. Novels and most non-fiction should be reflowable, letting the reader resize text freely. Fixed layout is reserved for children's picture books, cookbooks and heavily designed pages. Before any store sees the file, it should pass EPUBCheck, the industry's automated validator.
The ebook is not a PDF of your print book. It is closer to a small website packaged in one file, and the packaging rules are strict enough that stores automatically reject files that break them.
Reflowable or fixed layout?
| Reflowable | Fixed layout | |
|---|---|---|
| Text behaviour | adapts to screen and font size | locked, like a printed page |
| Best for | novels, memoir, business books | picture books, cookbooks, art books |
| Accessibility | excellent, reader controls everything | limited by design |
| File complexity | lower | high, per-page control |
The rule of thumb: if your book is mostly text, reflowable is correct. If the position of every element on the page carries meaning, fixed layout is the honest choice. The trade-offs run deeper than this table, and Librum's journal piece Reflowable vs fixed-layout EPUB walks through edge cases like poetry and textbooks.
Yes, Kindle takes EPUB now
Amazon retired its old MOBI pipeline: KDP has accepted EPUB uploads for years now and converts them internally to its own delivery format. In practice this means one well-built EPUB 3 file serves Amazon, Kobo, Apple, Google and library platforms, which is exactly why building it properly once beats exporting five approximations.
What EPUBCheck catches
EPUBCheck is the open-source validator the industry treats as the entrance exam: broken internal links, malformed metadata, missing table-of-contents entries, images that are referenced but absent, HTML that readers will render unpredictably. Stores run equivalent checks at ingestion, so a file that fails EPUBCheck is a file that will bounce, sometimes days later, when your launch is already announced. Every ePUB Librum ships is EPUBCheck-validated first; the details are on the eBook production service page.
One EPUB 3 file, validated, that works on Kindle, Kobo, Apple Books and 10+ readers: Librum builds it from your manuscript from €100. See the ePUB service
Frequently asked questions
What is the difference between reflowable and fixed-layout EPUB?
Reflowable EPUB lets text adapt to any screen size and any font setting the reader chooses, which suits novels and most non-fiction. Fixed layout locks every element in place like a printed page, which children's picture books and design-heavy titles genuinely need, at the cost of flexibility.
Does Kindle accept EPUB files?
Yes. Amazon KDP accepts EPUB uploads and converts them internally to its delivery format, having retired the old MOBI route. A single well-built EPUB 3 file can therefore serve Amazon, Kobo, Apple Books, Google Play and library distribution platforms simultaneously.
What is EPUBCheck and do I need to pass it?
EPUBCheck is the industry's automated EPUB validator, and effectively yes: retailers run the same class of checks when you upload. A file that fails EPUBCheck will typically be rejected at ingestion or render unpredictably on some devices, so validation before submission saves launch-week surprises.
Related: What is a print-ready PDF and How to self-publish in the UK.
