Estimating the Size of an Index
From Indexing Books by Nancy C. Mulvany. pp. 65-67.
Reprinted with permission of The University of Chicago Press.
© 1999 by The University of Chicago. All rights reserved.
Occasionally there is little space available for an index not because of a conscious decision to reduce access to
information in the text but, rather, because of poor planning. During the book design phase, ideally an appropriate
number of pages will be reserved for the index. The designer can work with straightforward percentage numbers.
Table 3.2 gives the percentage of index pages allotted along with a rough estimate of index entries per page for
various types of books.
The very general nature of the figures in the table is revealed when we examine two indexes. The index of the
January 1967 edition of The Joy of Cooking occupied 60 pages of the book; the indexable text took up 787
pages. This is an 8% index. All who have used this index know that it is dense. Terms are often double- and
triple-posted. Cross-references abound.
On the other hand, Greenhouses: Planning, Installing, and Using Greenhouses, published by Ortho Books
(1991), includes a 3% index. On the face of it, one might assume that the book is not thoroughly indexed or that the
indexable text is not as dense as in The Joy of Cooking. On the contrary, this book is very densely indexed. The
indexer reports that there is an average of 8.6 entries per page. The figures for entries per page in table 3.2
demonstrate that this index would fall into the Technical Documentation I category, which often has 10 percent indexes.
The critical difference between these two indexes is a matter of typography and layout. The Joy of Cooking
index is set in 8-point type with 9-point leading at two columns per page, on a six and one-half inch by eight and
three-quarters inch page. The Greenhouses index is set in 7-point type with 9-point leading at four columns per page,
on an eight and one-half inch by eleven inch page. It is important to keep in mind that even when an adequate number of
pages are not available for the index, it is still possible to provide a thorough index. The wizards in the production
department have a variety of options available to fit a large number of index entries on a page.
The problem with setting up a table like table 3.2 is that some editors and indexers will consider the numbers
immutable. Every book must be evaluated on its own terms—and according to its readers' needs. Some medical textbooks
will need a 10 percent index, not a 7 percent index. If a 10 percent index is called for, then a 10 percent index
should be created.
. . . If an indexer suspects that an index will need more space than has been assigned, it is the indexer's duty to
bring this matter to the editor's attention as soon as possible so that the production department will have the lead
time to consider changing the layout of the index pages. The indexer would do well to keep a running tally of entries
per page as the work progresses.
To summarize, before indexing begins, the indexer must determine what major sections of the text will be indexed and
which sections, if any, will not be indexed. The publisher's style requirements must be clearly understood. The indexer
must have at least a general notion of the space that will be available for the index.