_Fold symbol._ _Size letter._ _Outside height._
Never use for size. Never use for fold. In centimeters.
48º Fe Up to 10
32º Tt 10 – 12.5
24º T 12.5 – 15
16º S 15 – 17.5
12º D 17.5 – 20
8º O 20 – 25
4º Q 25 – 30
fº F 30 – 35
F⁴ 35 – 40
F⁵ 40 – 50
Prefix _nar._ if width is less than ⅗ height.
Prefix _sq._ if width is more than ¾ height.
Prefix _ob._ if width is more than height.
For all books over 35^{cm} high the superior figures show in which
10^{cm} of height the book falls, e. g., F⁸ is between 70 and 80^{cm}
high.
_Actual size method._
Give all sizes in cm (for greater accuracy adding decimals), leaving
the old symbols and names, 8º and Octavo to indicate fold only. Give
height first, followed by h, or by × and width, e. g., 23^h or 23 ×
14. 23^h means between 22 and 23, i. e., in 23^d cm. All measures are
taken outside the cover. Width is from hinge to edge not including the
round. To measure paper or letter-press, prefix p(aper) or t(ype) to
figures, including in type neither folio nor signature lines.