Duodecimo
Book & Publishing Formats · 5 specs
Direct Answer
A Duodecimo (abbreviated 12mo or 12°) is a classical pocket book format created by folding a printer's sheet into 12 leaves (24 printed pages). Measuring approximately 4.75 × 7.5 inches (120 × 190 mm) or 5.0 × 7.75 inches, it was the historical ancestor of the modern paperback, widely used for personal devotional books, poetry collections, and traveler guides.
Source: Bibliographical Society / Antiquarian Booksellers Association · Last reviewed Aug 28, 2026
Specs
| Folding Structure | Complex combination fold (often folding in thirds then quarters) |
| Leaf and Page Yield | 12 leaves (24 printed pages per sheet) |
| Typical Dimensions | Approx. 4.75 × 7.50 inches to 5.0 × 7.75 inches (120 × 190 mm to 127 × 197 mm) |
| Historical Significance | Aldine Press Renaissance pocket classics (Aldus Manutius, Venice, 1501) |
| Modern Equivalent | B-format paperbacks (5.1 × 7.8 in / 129 × 198 mm UK standard) |
The Renaissance Pocket Revolution
In 1501, Venetian master printer Aldus Manutius revolutionized European literacy by printing Greek and Latin classics in 12mo format combined with the newly invented Italic typeface. This made it possible for scholars, travelers, and students to carry classical philosophy and poetry inside a coat pocket rather than consulting chained library folios, at a scale European printing had not achieved before.