Quarto is a book or pamphlet produced from full 'blanksheets', each of which is printed with eight pages of text, four to a side, then folded twice to produce four leaves. Each printed page now presents as one-fourth size of the full blanksheet.The earliest known European printed book is a quarto, the Sibyllenbuch, believed to have been printed by Gutenberg in 1452–53, before the Gutenberg Bible, surviving only as a fragment. Quarto is also used as a general description of size of books that are about 12 inches tall, and as such does not necessarily indicate the actual printing format of the books, which may even be unknown as is the case for many modern books. These terms are discussed in greater detail in Book sizes.
