Rare Books
Book collecting guide

Guide to book formats


A book’s format refers to the shape and dimensions of the physical book.  When browsing bookseller catalogs and listings on the Internet, the terms and abbreviations used to describe book sizes (8vo, 12mo, folio, quarto, etc.) can seem confusing at first, but this page will help define a super octavo from a royal octavo.

Essentially these terms are simply an explanation of the book’s evolution from single sheets of paper into a completed book with printed pages. Each term defines how many times the initial piece of paper was folded to become pages.  Using this terminology, the term ‘Folio’ would tell us that the original sheet of paper was folded once, resulting in two leaves.  Therefore a book described as ‘Quarto’ would have its original sheet folded twice and would have four leaves - each leaf being one-quarter or one fourth the original size.

Armed with this knowledge, you can determine the approximate size of any book based on the publishing format.  Please note - the size is only an approximation because not every sheet of paper is exactly the same size. However these terms provide an essential guideline.

To make life even simpler, remember ‘Folio’ is a large upright-shaped book and an ‘Octavo’ is a small upright-shaped book, while a ‘Quarto’ is in-between the two and mostly square-shaped.  

Fold SymbolNameOutside height (inches)
-miniatureLess than 2" x 1.5"
64mosexagesimo-quarto2 x 3
48moquadragesimo-octavo2.5 x 4
32motricesimo-secondo3.5 x 5.5
18mooctodecimo4 x 6.5
16mosextodecimo5 x 7.5
12moduodecimo5 x 7.375
12mo (large)duodecimo5.5 x 7.5
8vocrown octavo6 x 9
8vooctavo6 x 9
8vomedium octavo6.125 x 9.25
8voroyal octavo6.5 x 10
8vosuper octavo7 x 11
8voimperial octavo8.25 x 11.5
4toquarto9.5 x 12
fo.folio12 x 19
fo.elephant folio23" to 25"
fo.atlas folio25" to 50"
fo.double elephant folio50" +