The term Quarto refers to a book size composed of sheets of paper obtained by folding a whole sheet twice to form four leaves or eight pages. Each piece would be one fourth size of a sheet. It also refers to a book or manuscript of the second largest standard size, usually measuring 32 cm (12 1/2 inches) in height, and 24 cm (9 1/2 inches) in width.  The plural form of Quarto is quartos and is abbreviated as q., Q., qto, Qto, and 4to.