Book size is a term used to describe the physical size of a book. Octavo (6 letters) is a book size that is 8vo, or 8 inches tall. Twelvmo (8 letters) is a book size that is 12mo, or 12 inches tall. Quarto (6 letters) is a book size that is 4to, or 4 inches tall. FOLIO (5 letters) is a book size that is fol., or 15 inches tall. Foolscap (8 letters) is a book size that is foolscap, or 13.5 inches tall. Duodecimo (9 letters) is a book size that is 12mo, or 12 inches tall. ELITE (5 letters) is a book size that is el., or 10.5 inches tall. Sexto (5 letters) is a book size that is 6to, or 6 inches tall.