This is my attempt to help readers even more ~ following on from my chatter on leaves and pages [115136].
So here goes, once again ~ please drop me a line if I am wrong!
For codex binding a single sheet of paper is folded in half to make a folio. A folio has four sides ~ or pages (provided a page is clearly understood to be one side of a leaf ~ as if numbered as in a book). There is always confusion about the understanding of the word page ~ as in "Turn over the page" which could mean "You are looking at page 20....now look at page 23" ~ or "21-22" ~ or "20-22" ~ or "21-23" ~ or "20,21-22,23". That example is perhaps trivial. The comments of people who buy notebooks on line and end up with half as many "pages" as they expect make it more serious. Sellers beware ~ do not advise "40 pages" if your customer expects "40 leaves".
Once the folios are collated and gathered into sections ~ many people call them signatures ~ it is helpful to refer to the number of leaves ~ where a leaf is the two sides containing obverse and reverse pages. That gives two leaves to a folio. In the paragraph above I started with one sheet ~ and now it has become two leaves or four sides!
So ~ for general use ~ I would suggest 'This book has twenty leaves which provides forty pages if they are numbered as in a book.' Maybe better still avoid the use of page 'This book has twenty leaves which provides forty sides'.
For bookcrafters I might say 'Four sections of six folios (equals 24 folios) ~ which is 48 leaves ~ which is 96 pages'. Maybe 96pp would be better ~ it is a widely recognized abbrevation.
I may have caused confusion here ~ the intent is to avoid confusion between other people. You may be quite clear as to what you say ~ the listener may have an equally clear understanding of something else.