Publishers and librarian almost always state the length of a printed book in pages. Some works may also count words. The length of a page depends on the size of the printed characters, the margins and the line spacing, as well as the area of the page.
The size and shape of a character is determined by the typeface, the font, and the font size. For the metal type used in print printed page, the basic font size is measured in points. A desktop publishing point is 1/72 of an inch (0.3527 mm). The publishing industry considers 12 points (i.e. 1/6 inch; 4.234 mm, just less than 0.5 cm) to be a visible height for the standard reader. However some font in printed work are 10 or 9 points high, and some text (e.g. superscipts, subscripts, footnotes, endnotes) is smaller.
Librarians shelve some printed works as “large print“. The font is usually 18 points high, but the American National Association for Visually Handicapped (NAVH) standard for its approval mark is 14 points.