Duodecimo (12mo) is a book size formed by folding a sheet of paper twice and creating four leaves, or eight pages, from it. These half sheets are then cut along their fold line into two pages each for printing a book in duodecimo size.
Duodecimo derives its name from the Latin for twelve, duodecim. This size became increasingly popular during Europe’s late Middle Ages and Renaissance for producing small books such as devotionals or prayer books – often used for personal journals or diaries.
Modern duodecimo books are mass-produced paperbacks. In the UK, such books typically measure four inches wide by six inches tall; mass-market versions in America naturally come with dimensions five inches wide by eight inches high.
Duodecimo books may often be mass-produced, but they can also be made as limited edition, hand-bound books of higher quality – typically featuring high-quality paper and bindings – by small presses or individual bookbinders.
Duodecimo books are typically printed on both sides of the paper to produce 32 pages on each sheet, using perfect binding technology. After cutting to size and adhering them to the spine of their book cover spine, excellent bound duodecimo books become perfect bound.
Duodecimo books are typically associated with mass-market paperbacks; however, they can also be bound in various ways, including case binding, perfect binding, and saddle stitching. Hardcover books usually opt for case binding; mass-market paperbacks utilize perfect binding, while magazines typically opt for saddle stitching.
Duodecimo books were widely popular during the sixteenth and seventeenth centuries before falling out of fashion in the eighteenth. Today, they remain a niche product among collectors of antique books.