On a normal book page, about 250-300 words fit on a page. This, of course, depends on the font, but that's the standard. So a 40,000 word novel would be about 130 pages in a standard book.
STANDARD NOVEL WORD COUNT ACCORDING TO ITS GENRE
Young Adult Novel – 60,000 words
Memoir Novel – 80,000 words
Literary Fiction or General Fiction – 80,000 words