On GR: click the "page number" in the status update and it'll change to % which is much easier to guesstimate (it's not like anyone will care if you're a % or two off on GR
Re ebook page numbers on GR: There are specific (and typical for cataloguing in libraries) rules about which pages get counted and which don't (for instance, advertising etc at the end of books are routinely discarded, as are initial roman numeral enumerated numbers.) The actual rules are in the librarian guidelines, but they are essentially the same as Worldcat (which means the same as libraries use). But they are always edition specific, and can change even between reprintings because a tiny typo fix in a later printing caused the entire text to be reflowed and rejustified to add or remove a page - or several, if the first edition was badly copyedited.
JSWolf: the librarians aren't staff, they're volunteers, and if you don't say where you got the page numbers, they won't add them. And because they are edition specific, if you don't specify the exact edition you mean by ISBN, they won't get added.
Acceptable sources for ebook page counts on GR are three: The publisher (if they bother giving one on their website, but this is most often just the paperback page count anyway, and probably the least accurate one), Worldcat (because librarians) and the estimate from the Calibre page count plugin - but that last will only be accepted if you say that's where you got it from and it will be replaced if anyone ever notices one of the first two although that's unlikely to happen.