A feature not to be overlooked in the appearance of a well-printed
book is that of the margins. The perfect type-page is supposed to be
proportioned in such a way that its diagonal is twice its width. With
this page as a basis, the location of the type upon the paper leaf is
to be studied carefully. In general, the two pages, right and left,
should be considered as a unit, and the top margin and the inside
margin of each page should be approximately the same. Doing this, the
total blank between the two pages is supposed approximately to equal
the outside and the bottom margins.
The proportion of margin is, to a certain extent, dependent upon the
size of the book, the margins becoming greater as the volume increases
from the thirty-two mo size up to the folio. A student of typography
has ingeniously estimated that, taking the height of the paper leaf
as 100 units, the height of the type page of the ordinary trade book
should be from 72% to 75%; that of a library edition, from 66% to 71%;
that of a de luxe volume, from 60% to 65%.