A reflowable EPUB lets the reading system repaginate text to fit any screen and any font size. A fixed layout EPUB pins content to fixed dimensions and produces exactly one page per file, like a PDF. Reflowable is the default and is what a novel should be. Fixed layout exists for books where position carries meaning, such as picture books and complex non-fiction.
The Distinction Is Formal, Not Stylistic
This is set by a single metadata property in the package document. The EPUB 3.3 specification defines exactly two values for rendition:layout:
reflowable, which the spec defines as content that "is not pre-paginated (i.e., reading systems apply dynamic pagination when rendering)", and notes is the "Default value."pre-paginated, content that "is pre-paginated (i.e., reading systems produce exactly one page per spineitemrefwhen rendering)."
Note the spec's own word is pre-paginated, with a hyphen. "Fixed layout" and "FXL" are the industry names for the same thing.
Because reflowable is the default, a file that declares nothing is reflowable. You do not add anything to get it.
The reading system side is equally strict. Where the property is pre-paginated, reading systems "MUST produce exactly one page per spine itemref when rendering".
Fixed layout also requires real dimensions, and the spec is specific about where they come from: the height and width must be in the first viewport meta tag in the document, and "reading systems will ignore subsequent viewport meta tags". Setting the size in CSS instead does not work.
The Accessibility Cost Is in the Spec Itself
This is not an opinion held by accessibility advocates. It is a warning written into the specification:
"Reading systems typically restrict or deny the application of user or user agent style sheets to pre-paginated documents because dynamic style changes are likely to have unintended consequence on the intrinsic properties of such documents. EPUB creators should consider the negative impact on usability and accessibility that these restrictions have when choosing to use
pre-paginatedinstead of reflowable content."
In plain terms: a reader who needs larger text often cannot get it in a fixed layout book, because the reading system disables the controls that would break the layout.
The DAISY Consortium, which maintains accessible publishing guidance, recommends reflowable "when a publication has to be broadly accessible", and lists the recurring failures: reading order that follows visual placement rather than sense, content fragmented across pages, images of text with no alternative, and content that cannot be zoomed without scrolling.
Which One Do You Need
Reflowable for anything that is fundamentally a stream of text: novels, memoir, most non-fiction, poetry in most cases. If the reader can change the font size without the book losing meaning, it should reflow.
Fixed layout where position carries meaning: children's picture books, comics and graphic novels, cookbooks and illustrated references with tightly bound text and image, anything with complex tables or diagrams that cannot survive reflow.
A novel does not need fixed layout. Choosing it costs the reader font control and gains nothing.
A Genuine Trap in Amazon's Documentation
Amazon's fixed-layout help page shows an example using prepaginated, without the hyphen. That is not a legal value. The spec defines pre-paginated, and Amazon's own description column on the same page says so correctly while the example contradicts it.
Amazon also documents proprietary alternatives, fixed-layout and original-resolution as bare meta names, which have no standing in EPUB 3 and mean nothing to other retailers.
There is one further divergence worth knowing. Amazon states that a book cannot be partly reflowable and partly fixed. The specification explicitly permits it, via per-spine-item overrides. Mixed files are valid EPUB; they are simply not accepted by Amazon.
If you are hand-editing, follow the specification and validate. If you copy Amazon's example verbatim you get an invalid file.
What Deckle Produces
Deckle exports reflowable EPUB. It does not set rendition:layout, which under the specification means the default applies, and the default is reflowable.
That is the correct output for a novel, and it is why Deckle's EPUB adapts to the reader's font size and screen. There is no fixed-layout export, because the format exists for picture books and illustrated references rather than for prose.
If you need fixed layout for an illustrated project, that is a job for dedicated layout software, not a setting to look for here.
For what retailers require on top of the specification, see Amazon KDP EPUB requirements, and for the styling that survives reflow, styling your EPUB. For how the format compares with the alternatives, see EPUB vs PDF vs DOCX, and for what goes into the container, how to make an EPUB file.
Common Mistakes
- Choosing fixed layout to preserve your typography. It removes the reader's font control, and the spec warns about the accessibility cost.
- Copying Amazon's
prepaginatedexample. The legal value ispre-paginated. - Setting fixed dimensions in CSS. They must be in the first
viewportmeta tag. - Using Amazon's proprietary metadata names. They mean nothing to Apple, Kobo or Google.
- Assuming mixed layouts are invalid. The spec allows them; Amazon does not accept them.
- Adding a declaration to make a file reflowable. Reflowable is the default already.
FAQ
Q: Which should a novel use? A: Reflowable, without exception.
Q: Does fixed layout look better? A: It looks more controlled on the device you designed for, and worse on every other one, because it cannot adapt.
Q: Can one book be partly fixed? A: Under the specification, yes, per spine item. Amazon does not accept it.
Q: Is fixed layout the same as a PDF? A: Similar in effect, since both pin content to a page. A fixed layout EPUB is still an EPUB, with the container and metadata that implies.
Q: How do I check which one my file is?
A: Look for rendition:layout in the package document. If it is absent, the file is reflowable.