sexagesimo-quarto

A sexagesimo-quarto, or 64mo, is a book size produced by folding a large sheet of paper six times, creating 64 leaves or 128 pages in the finished gathering. The resulting page dimensions typically fall between 1.87 and 2.5 inches in width and 2.5 to 3.125 inches in height, depending on the original sheet size and press configuration. This makes it one of the smallest practical book formats ever manufactured, suitable only for pocket editions, miniature reference works, or novelty volumes.

The term comes from the Latin sexagesimo-quarto, meaning "in the sixty-fourth," which describes the mathematical relationship: an unfolded sheet divided into 64 parts. Each successive fold halves the page count. Starting with a full sheet (1 leaf), one fold produces a folio (2 leaves), two folds create a quarto (4 leaves), three folds yield an octavo (8 leaves), and so on through sextodecimo (16), trigesimo-secondo (32), and finally sexagesimo-quarto (64). This nomenclature dates to hand-binding practices and remains embedded in printing specifications despite modern industrial production.

Sexagesimo-quarto books presented real manufacturing challenges. Paper had to be of high quality and thin enough to accommodate six folds without cracking or splitting. The gathering itself became difficult to handle and collate by hand; bindery equipment designed for common formats like octavo or duodecimo required substantial adjustment. Presswork demanded precise registration across six folding stages. For these reasons, the format remained confined to specialized work: diplomatic miniatures, pocket almanacs, tiny prayer books, and occasionally children's books where physical smallness was the entire marketing point.

By the early 20th century, sexagesimo-quarto had fallen almost entirely out of commercial use. Modern offset printing, with its reliance on sheet-fed and web-fed machinery calibrated for standard sizes, has no native accommodation for such extreme reduction. Today the term survives mainly in historical bibliography and in the specialized world of fine press printing, where occasional hand-binders reproduce such formats as historical curiosities or bespoke commissions. Any contemporary sexagesimo-quarto book is a deliberate, labor-intensive exception rather than an economic production choice.