How Long Should My Index Be?

by Nancy Humphreys on August 9, 2011

I received a compliment today about the index for my new guide, Marketing Your Book to Libraries: “The size of your index makes me think your book is 2,000 pages!”

When I explained that my book had a lot of detail, and it was intended to be used as a “reference” book, this person added, “If a person buys a book as a ‘text’ or ‘reference’ book they would kill for an 8% index.”

So I thought I would blog today about how much space a print-book index should take.

Typical index length

A typical index for an ordinary book takes up about 5% of the pages. That’s an index for a 100-page book that’s 5 pages long. But many books are not typical.

Library reference books and some guidebooks are often much more detailed. An 8% index is more typical for those. That’s an index to a 100-page book that’s 8 pages long.

And, contrary to what you might think, some textbook indexes might take up less than 5% of the space in a book. Those textbooks are ones for introductory courses in high school and/or college.

The purpose of these textbooks is to help students learn the basic terminology for the subject field of the textbook. As a result, a usual function of an index – bringing together in one place all important mentions of a topic that are scattered throughout the book –  doesn’t come into play with a “101-type” textbook. Its index might only include a single page after most headings. This page is where a student can find the primary definition for each term.

That’s why introductory textbook indexes can be very brief, contain few subheadings, and provide no See also cross-references among the terms.

But that kind of abbreviated indexing is a “sin” when it comes to advanced textbooks and educational trade books intended for reading by the general public!

Estimating the number of pages for your index

Nancy Mulvany’s classic guide to indexing contains a section on sizes of indexes. Table 3.2 on page 72 of the second edition gives “estimates of percentage of index pages and entries per page by type of book.”

The percentage of pages by type of book ranges from 2 to 15 or more pages. The number of index entries that the indexer will need to create per page can run from 3 to 10 or more entries. This is quite a wide variety!

The phrase, “type of book” refers to genres of books such as cookbooks, textbooks, technical manuals, etc. as well as to the audiences for books, e.g., children’s books, trade books, scholarly books. etc.

As you might have guessed, the type of book you have greatly impacts the price for its index. Even within a specific genre of books there is considerable variation in the size of the index and amount of time indexing will take.

For example, computer books usually have very dense indexes, but some are way more dense than others. A new operating system, for example, will require a very comprehensive index to introduce readers to new features of the OS while covering the older features for users who aren’t yet aware of them.

That’s why I’d recommend you ask for an indexer’s opinion before you decide upon a size limit for your index. Or just leave the determination of index size of the up to the indexer. That’s often easiest for everyone involved!

(The link for Mulvany’s Indexing Books, 2nd ed., The University of Chicago Press, 2005 is

Note: this is not an affiliate link. Amazon canceled all California affiliates after the state demanded that Amazon tax all books sold in California. Amazon canceled its California affiliates so that it would not qualify as having a “business presence” in California. Amazon is encountering similar tax demands by other states.)

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For information about my new PDF book, Marketing Your Book to Libraries: An insider’s Guide for Authors by Nancy K. Humphreys, see Early-bird discount available until September 2011.

Marketing Your Book to Libraries Marketing Your Books to Libraries: An Insider's Guide for Authors by former librarian Nancy K. Humphreys includes: 
  • How to tell what kind of library to target
  • Types of librarians and books they order
  • Strategies to get past the "gatekeepers" who influence librarians
  • Right ways to approach librarians most likely to order your book

Learn more »

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