The name indicates the number of pages in the sheet, thus: in folio book, 4 pages or 2 leaves = 1 sheet; a quarto, or 4to., has 8 pages or 4 leaves to a sheet; an octavo, or 8vo., 16 pages or 8 leaves to a sheet. In a 12mo., 24 pages or 12 leaves = 1 sheet, and the 18mo., 36 pages, or 18 leaves = 1 sheet, and so on. The following are the approximate sizes of books:

Royal Folio

19 inches

X 12

Demy

18 "

X 11

Super Imp. Quarto (4to)

151/2 "

X 13

Royal 4to

.121/2 "

X 10

Demy 4to

.111/2 "

X 81/2

Crown 4to

11 "

X 8

Royal Octavo

101/2 "

X 61/2

Medium 8vo

. 91/2 "

X 6

Demy 8vo

9 "

x 51/2

Crown 8vo

7 1/2 "

X 41/2

Foolscap 8vo

7 "

X 4

12 mo

7 "

X 4

16 mo

. 61/2 "

X 4

Square 16mo

. 41/2 "

X 31/2

Royal 24mo

51/2 "

X 33/4

Demy24mo

5 "

X 23/4

Royal 32mo

5 "

X 3

Post32mo

4 "

X 21/2

Demy 48mo

33/4 "

x 21/4