There can be much confusion over the words sheet ~ leaf ~ page. Often it does not matter and is easily clarified by the context. Be aware that here can easily be a misunderstanding on WWW-sales sites.
Advertising a book as having of '80 pages' upsets a buyer who expects a page to be two sides of paper. It may sound odd ~ but I have seen numerous complaints in the comments columns from people who expect ~ or hope for ~ twice as much as they will receive. To avoid accusations of dishonesty, listings have to be carefully compiled.
I try to use a phrase such as 'pages ~ as if numbered in a book', or else spell out my understanding of the various words. Maybe I make it even more complicated by introducing the words folio and section.
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 if they are numbered as if in a book.
Once the folios are collated and gathered into a section ~ many people call them signatures ~ it is tempting to refer to the number of sheets ~ where a sheet is the obverse and reverse pages. That gives two sheets to a folio. In the paragraph above I started with one sheet ~ and now it has become two! Best not to use sheet at this stage ~ especially when the word leaf is available.
So ~ for general use ~ I would suggest 'This book has twenty leaves which provides forty numbered pages.'
For bookcrafters I might say 'Four sections of six folios (equals 24 folios) ~ which is 48 leaves ~ which is 98 pages'. Maybe 98pp would be better ~ it is a widely recognized abbrevation.