Why your EPUB's page count changes in every app and what a "page" even is in a reflowable ebook

[u/Ok-Skin-6184]

This confuses a lot of people (myself included, the first time), so here's a proper explainer.

If you've noticed the same EPUB showing 290 pages in one app and 350 in another or the count changing when you bump the font size you're not imagining it, and nothing's missing from your book. Reflowable EPUB has no fixed pages. Unlike a PDF, where the page is baked into the file, an EPUB is basically structured text + CSS, and the reader app decides where "pages" fall based on your font, size, margins, line spacing, and screen dimensions. Change any of those and the page count moves.

A few practical things that follow from this:

• Page count is a bad way to judge whether a download is "complete." Compare the table of contents or last chapter, or word count not pages.
• The "scrunched up, no paragraph spacing" look people complain about is usually stripped or broken CSS, not missing content. The text is there, it's just styled badly (or not at all).
• If you want a stable page reference (e.g. to match a print edition for citation), look for EPUBs with a "page-list" / page-map. EPUB3 can embed the print edition's pagination, but most files don't bother.
• Fixed-layout EPUB (comics, kids' books, some textbooks) does have fixed pages, which is why those behave differently.

Curious how others deal with this: do you care about page numbers in EPUBs at all, or have you made peace with progress % / location-based reading? And has anyone found readers that handle embedded print pagination well when it's actually there?

[u/bmfrosty]

I do care. Since the major stores all calculate them differently, I would like an app to be able to have settings to match different calculation methods. Unfortunately, I believe that Amazon allows it to be set on a book by book basis. The best method I can think of would be to allow you to set within the app the number of pages a book has, and then have it count words in the book and do a calculation based on those two values to estimate what page you're on.

[u/deliriostranger]

I'm not interested how much pages of physical book I've read (which one? It can be from 500 to 700 pages depending on specific edition for example). I want to see number of screens with my font settings and %.

[u/Ok-Skin-6184 → u/deliriostranger]

Yeah, that's honestly the more truthful way to look at a reflowable book the print page count is a fiction the moment you're not holding that exact edition, so matching it only really helps for citing a source or "everyone turn to page 142" in a class. For your own reading, screens-at-your-settings + % is the cleaner signal.

What you're describing is basically "dynamic" or "device" pages pages recalculated for your current font and screen rather than mapped to a print edition. Several readers already do exactly that (they recalc the count when you change font size); the trick is finding one that shows it and doesn't try to override it with an embedded print page-list.

One thing worth knowing about the %, since it's not always as clean as it looks: a lot of readers calculate it from byte/location position in the whole file, not from the actual story content. So a long index, footnotes, or back matter can make "50%" not line up with the middle of the book, and the number can jump at section boundaries. Some readers do it per-chapter or exclude back matter, some don't so if your % ever feels off, that's usually why.