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Information on Indexing

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.



Type of Book Percent of
Index Pages
Entries per Page

Mass market trade books
Light text, not heavy on details
2-5% 3-5
General reference books
Medical texts
Scholarly texts
Style manuals
7-8% 6-8
Technical Documentation I
General end-user manuals
Introductory manuals
Policy and procedures manuals
Training manuals
10% 8-10
Technical Documentation II
Codes & regulations
Service & repair manuals
Specialized audience material
Systems manuals
Theory of operations
15% + 10+