Glossary
EPUB
EPUB: EPUB is the open standard file format for ebooks, used by every major store and reader except Amazon’s internal format, which KDP now creates from an EPUB upload. An EPUB is a zipped package of HTML, CSS and images with a navigation file, which lets text reflow to any screen size and font setting.
Why stores want EPUB
Because it reflows. A PDF is a fixed picture of a page; an EPUB is the text plus instructions, so a phone, a tablet and a Kindle each lay it out at their own size. KDP, Kobo, Apple Books and Google Play all accept EPUB directly, and KDP recommends it over DOCX for predictable results.
What a good EPUB contains
- A linked table of contents (the navigation document) so readers can jump between chapters.
- One HTML file per chapter with real headings, not bold text.
- A cover image declared as the cover, at least 1600 pixels tall.
- Metadata: title, author, language, identifier.
- Images sized for screens, to keep the delivery fee low on Amazon.
How to make one
Word processors export EPUB with mixed results. Calibre, Vellum, Atticus and Scrivener build clean files from a manuscript. AI ebook generators such as create-ebook export an EPUB alongside the PDF and DOCX, already validated for KDP. Whatever the tool, check the file in the KDP previewer or in Apple Books before publishing.
Frequently asked questions
Is EPUB the same as MOBI or KPF?
No. MOBI was Amazon’s older format and is no longer accepted for new uploads. KPF is what Kindle Create produces. EPUB is the format to keep as your master.
Can I convert a PDF to EPUB?
Technically, with Calibre, but the result is usually poor: PDF has no structure to reflow. Convert from DOCX or build from the source instead.
Does an EPUB need an ISBN inside it?
It needs an identifier, which can be an ISBN, a UUID or a URL. Stores use their own identifier anyway.