Duodecimo, or 12mo, is a book size resulting from folding a sheet of paper twice to create four leaves, or eight pages. Each leaf, or half-sheet, is then cut along the fold to create two leaves, or four pages. When a book is printed in this size, it is said to be in duodecimo.
The term duodecimo comes from the Latin word for twelve, duodecim. This size became popular in Europe in the late Middle Ages and the Renaissance for the production of small, portable books, such as devotional books and prayer books. Books printed in duodecimo were also frequently used as personal journals and diaries.
In the modern era, duodecimo books are generally mass-produced paperbacks. In the United Kingdom, paperbacks that are approximately four inches wide and six inches tall are often referred to as “pocket books.” In the United States, mass-market paperbacks are typically five inches wide and eight inches tall.
While duodecimo books are often mass-produced, they can also be produced as limited edition, hand-bound books. These books are generally of a higher quality, with higher-quality paper and bindings. They are often produced by small presses or individual bookbinders.
Duodecimo books are typically printed on both sides of the paper, resulting in 32 pages per sheet. This printing method is called perfect binding. The pages are then cut down to size and glued to the spine of the book cover.
While duodecimo books are typically associated with mass-market paperbacks, they can be bound in a variety of ways, including case binding, perfect binding, and saddle stitching. Case binding is the most common type of binding for hardcover books. Perfect binding is often used for mass-market paperbacks and saddle stitching is often used for magazines.
Duodecimo books were popular in the sixteenth and seventeenth centuries, but fell out of favor in the eighteenth century. Today, they are considered a niche product, and are most popular among collectors of antique books.