The size of a specific book is measured from the head to tail of the spine, and from edge to edge across the covers. However, in bookbinding, printing, and publishing, a series of terms are used to indicate the approximate size of a book. These terms are derived from the number of leaves created from a standard size sheet of paper (19" x 25") when each signature of the book is printed. For example, a quarto book results when four leaves are created from each sheet of paper. The resulting book will be approximately 12.5" inches tall and 9.5" inches wide, before trimming. Each leaf usually has a printed page or an intentionally blank page on each side, so a quarto signature usually represents eight pages of the book. Octavo and quarto are the most common book sizes, but many books are produced in larger (folio) and smaller sizes as well. These terms are often abbreviated, using 4to for quarto; 8vo for octavo; and so on