Folio
Book & Publishing Formats · 6 specs
Direct Answer
A Folio (abbreviated 2° or fo) is a traditional book format created by folding a full printer's master sheet (Broadside) in half once, producing 2 leaves (4 printed pages). Measuring approximately 12 × 19 inches (305 × 483 mm) or larger, it is historically reserved for monumental prestige publications, including the Gutenberg Bible (1455) and Shakespeare's First Folio (1623).
Source: Bibliographical Society of America / Traditional Bookbinding Standards · Last reviewed Aug 28, 2026
Specs
| Folding Structure | 1 fold down the center of a full printer's sheet |
| Leaf and Page Yield | 2 leaves (4 printed pages per sheet) |
| Typical Historical Dimensions | Approx. 12 × 19 inches (305 × 483 mm) up to 15 × 20 inches |
| Signature Geometry | Broadside sheet folded into vertical folio signatures |
| Historical Milestone | Gutenberg 42-Line Bible (1455) / Shakespeare's First Folio (1623) |
| Modern Commercial Equivalent | Oversized coffee table art books, museum facsimile editions, archival atlases |
Historical Prestige and Display
In the Renaissance and early modern printing era, paper was the single most expensive material in book manufacturing. Publishing a work in Folio format was a declaration of supreme cultural or religious significance (such as royal statutes, Holy Bibles, and complete works of master dramatists). Due to their immense weight, folios were read resting on dedicated lecterns rather than held in hands.