Book History: F is for Folio

A folio is made by folding the paper or vellum one time to form two leaves or four pages.  Both sides of the leaves are used for writing or printing, so one fold makes four pages.  A group of folios could be sewn together to form a book.  Because paper was rather large and animal skins were also, a book made of folios was a large format book.  The sizes of the sheets were not standard, so there is not one measurement that is “folio size.”  Folio refers to the fact that the sheets were only folded once.  Once books were made using machine presses and paper became more uniform in size, folio was used to describe books that are taller than 30 cm (about 11 ¾ inches)) or wider than 23 cm (about 9 inches).  Folios are often shelved lying flat to put less stress on the hinges of the book. 

**Folio photo from the Folger Blog--The Collation  14 November 2011 entry