4to

4to, short for quarto, is a historical term used in book production and cataloging to describe a specific format of printed works. It denotes the method of folding a full sheet to create the book’s pages rather than signaling a precise measurement.

In the quarto format, a sheet is folded twice, producing four leaves per sheet (eight pages). The arrangement of pages follows standard early modern printing practices, and the term focuses on the physical form rather than exact dimensions. Because printers in different periods and regions used varying sheet sizes, 4to lacks a fixed height or width; sizes typically ranged roughly within the mid-sized spectrum of traditional book formats.

Historically, quarto was widely used from the 16th to the 18th centuries and for a broad range of texts, including plays, scholarly works, and popular literature. Many early editions of literary and scientific works appeared as quarto, and the format was favored for its portability and lower production costs compared with larger folio editions.

In cataloging and bibliographic references, 4to sits in a relative size hierarchy among traditional formats, generally larger than octavo and smaller than folio. While the term is still encountered in historical scholarship and library records, it is largely obsolete in modern publishing, where precise measurements and digital formats have replaced these descriptive size classifications.

See also: folio, quarto, octavo, duodecimo.