Why Books Are Named By Folds

Traditional book sizes like quarto or octavo actually describe how many times a sheet of paper was folded during printing. A quarto means a large original sheet was folded twice to create four leaves.

Printers once used these terms to tell you exactly how many pages a single large sheet of paper would produce. While we use these words today to describe physical height, they originally defined the complex mechanics of the printing press. Because modern manufacturing has changed so much, these classic labels are often inaccurate for newer books. It is a fascinating relic of an era when books were built like origami.