Book Sizes

   The names of book sizes are based on the old system, still widely used, of considering the size of a page as a fraction of the large sheet of paper on which it was printed. This system is illustrated in Table I below. In printing books, an even number (as 4, 8, 16, 32, 64) of pages is printed on each side of a single large sheet, which is then folded so that the pages are in proper sequence and the outside edges are cut so that the book will open. Except for the largest size, the folio, the name of the size indicates the fractional part of the sheet one page occupies (as octavo "eighth"). In this system, since the fractional name alone cannot denote an exact size, the name of the sheet size precedes the fractional name. Thus royal octavo is understood to designate a page one-eighth the size of a royal sheet, medium octavo a page one-eighth the size of a medium sheet, and crown octavo a page one-eighth the size of a crown sheet. But paper is cut into many sheet sizes and even the terms crown, medium, and royal do not always designate sheets of the same dimensions. Three of the more common sheet sizes have been selected: royal 20 x 25 inches, medium 18 x 23 inches, and crown 15 x 19 inches. Actual page sizes run a little smaller than calculations, since the sheets, when folded to page size, are trimmed at top, outside and bottom, the inside edge becoming part of the binding. British sheet size sometimes differs slightly from American. Table II illustrates the size names as they are used by the American Library Association, with only the octavo sizes including the name of a sheet size. The dimensional limits given in the table remain standard for this system. Table III gives equivalent terms and symbols for the size names.

Table I.

Size NameTimes Sheet FoldedLeaves to SheetPages to SheetSize of Page in Inches
royal folio12420 x 12½
royal quarto24812½ x 10
royal octavo381610 x 6¼
royal sixteenmo416326¼ x 5
royal thirty-twomo532645 x 3 1/8
royal sixty-fourmo6641283 1/8 x 2½
medium folio12418 x 11½
medium quarto24811½ x 9
medium octavo38169 x 5¾
medium sixteenmo416325¾ x 4½
medium thirty-twomo532644½ x 2 7/8
medium sixty-fourmo6641282 7/8 x 2¼
crown folio12415 x 10
crown quarto24810 x 7½
crown octavo38167½ x 5
crown sixteenmo416325 x 3¾
crown thirty-twomo532643¾ x 2½
crown sixty-fourmo6641282½ x 1 7/8

Table II
Scale of the American Library Association

Size NameSymbolOutside Height*Appx Size in Inches*
folioFover 30 cm12 x 19
quartoQ25-30 cm9½ x 12
octavoO20-25 cm6 x 9
   imperial octavoO-8¼ x 11½
   super octavoO-7 x 11
   royal octavoO-6½ x 10
   medium octavoO-6 1/8 x 9¼
   crown octavoO-5 3/8 x 8
duodecimoD17.5-20 cm5 x 7 3/8
duodecimo (large)D17.5-20 cm5½ x 7½
sextodecimoS15-17.5 cm4 x 6¾
octodecimoT12.5-15 cm4 x 6½
trigesimo-segundoTt10-12.5 cm3½ x 5½
quadrasegisimo-octavoFe7.5-10 cm2½ x 4
sexagesimo-quartoSfless than 7.5 cm2 x 3
*Outside height refers to the head-to-foot dimension of the book's cover
*Approximate Size refers to the front cover's rectangular dimensions

Table III
Size Names and Their Equivalents

OldModern - Preferred by PrintersAbbr.Symbol
foliofolio fo or f-
quartoquarto4to
sextosixmo6to or 6mo
octavooctavo8vo
duodecimotwelvemo12mo12°
sextodecimosixteenmo16mo16°
octodecimoeighteenmo18mo18°
vincesimo-quarto
vigesimo-quarto
twenty-fourmo24mo24°
trigesimo-segundothirty-twomo32mo32°
quadragesimo-octavoforty-eightmo48mo48°
sexagesimo-quartosixty-fourmo64mo64°
©Webster's Third New International Dictionary (1966)

Joyce Godsey's research adds: and she adds the following, from the Conservation Online web site:

BOOK SIZES

The dimensions of books, as measured, in inches, centimeters, or millimeters, from head to tail and from spine to fore edges of the cover. The descriptions given to book sizes are based on a still currently used system that involves using the size of a leaf as a fraction of the folded sheet on which it was printed. With reference to the printing of books, an even number of leaves always results when a sheet is folded, i.e., 2, 4, 8, 16, etc., resulting in printed pages on each side of the leaf, i.e., 4, 8, 16, 32, etc. Except for the largest size, the FOLIO (1) , the name of the size indicates the fractional part of the sheet one leaf occupies, e.g., quarto (2 folds, 4 leaves, 8 pages),¼ of the sheet; octavo (3 folds, 8 leaves, 16 pages), 1/8 of the sheet, etc. In this system, since books are printed from different sizes of sheets (See: BOOK BASIS), the fractional designation by itself cannot denote an exact size; therefore it is a common practice to give the name of the sheet before the fractional name, e.g., royal octavo, which is an octavo 1/8 the size of a sheet 20 X 25 inches or, excluding the SQUARES, a book 10 x 6¼ inches (before trimming). Paper is cut to so many sizes, however, that the terms crown, royal, post, etc., unless qualified, are practically meaningless. (See: SIZES OF PAPER). Untrimmed sizes for three commonly used sheet sizes are given below. The customary trim of 1/8 inch at head and tail will reduce the height of the text block by¼ inch; however, the size of the bound book. assuming 1/8 inch squares will make the height of the book the same as the sizes given. It should be mentioned that not all sheet sizes given are folded to produce books of the very small size indicated. All folds, following the first, are right-angle folds.

The common book-trade designation of sizes was originally related to a sheet of handmade paper measuring 19 X 25 inches, which was the common size of the papermaking mold. When folded to 8 leaves, or 16 pages, and trimmed, each was 6½ X 9¼ inches, approximately, and was the standard dimension of an 8vo. When folded to make 16 leaves, or 32 pages, it was a 16 mo. With the present great variety of paper sizes, all dimensions are by necessity only approximate. (52, 69, 140, 156, 169)

Book sizes

Size
(in inches)
NameTimes
Folded
Leaves
per Sheet
Pages
per Sheet
Size of
Untrimmed
Page (leaf)
25 by 38 folio 1 2 4 25 by 19
25 by 38 quarto 2 4 8 19 by 12½
25 by 38 octavo 3 8 16 12½ by 9½
25 by 38 sixteenmo 4 16 32 9½ by 6¼
25 by 38 thirty-twomo 5 32 64 6¼ by 4¾
25 by 38 sixty-fourmo 6 64 18 4¾ by 3 1/8
20 by 25 folio 2 4 20 by 12½
20 by 25 quarto 2 4 8 12½ by 10
20 by 25 Octavo 3 8 16 10 by 6¼
20 by 25 sixteenmo 4 16 32 6¼ by 5
20 by 25 thirty-twomo s 32 64 2½ by 3 1/8
20 by 25 sixty-fourmo 6 64 128 3 1/8 by 2½
18 by 23 folio 2 4 18 by 11½
18 by 23 quarto 2 4 8 11½ by 9
18 by 23 octavo 3 8 16 9 by 5¾
18 by 23 sixteenmo 4 16 32 5¾ by 4½
18 by 23 thirty-twomo 5 32 64 4½ by 2 7/8
18 by 23 sixty-fourmo 6 64 128 2 7/8 by 2¼

British book sizes

Size NameOctavo SizeQuarto Size
pott 6¼ by 4 8 by 6¼
foolscap 6¾ by 4¼ 8¼ by 6¾
crown 7½ by 5 1O by 7½
large crown 8 by 5¼ 10½ by 8
large post 8¼ by 5¼ 10¼ by 8¼
demy 8¾ by 5 5/8 11¼ by 8¾
post 8 by 5 10 by 8
small demy 8½ by 5 5/8 11¼ by 8½
medium 9 by 5¾ 11½ by 9
small royal 9¼ by 6 1/8 12¼ by 9¼
royal 10 by 6¼ 12½ by 10
super royal 10¼ by 6¾ 13½ by 10¼
imperial 11 by 7½ 15 by 11