Words per page in a published/printed book vary according to font, font size, and paper size. Anywhere around 300, or more, depending on the type of book. It has little to do with the standard word-count-by-page, which is based on a raw manuscript in Word with 12pt double-spaced Courier New and 1-inch margins, letter size (which has little to do with Word's word count, because it is a pre-computer age fossilized measure).
As for how many pages you would "lose" -- hell, who knows. As many as might make the stuff fit in the size of book the editor wants to put out, depending on font etc....