An important part of a nonfiction book proposal is providing information about your target audience. Hard numbers are most useful and most persuasive in convincing an agent or editor that there's a need for your book, so do some demographic research. If you're targeting homeowners, for instance, the U.S. Census Bureau can tell you how many people own their homes and how many people rent.

Your goal is to show that there's a large potential audience out there, just itching to pick up and purchase your book. Most publishers want to see a demonstrable market of at least 100,000 people. You can reasonably expect that between 1 percent and 10 percent of your potential readership will become aware of your book; for actual sales, assume that, at best, about 1 percent of your potential readers will buy your book.

Organizations and Associations

There are hundreds of thousands of social and professional organizations, and many of them might encompass the audience you're looking for. If your book is aimed at accountants, for example, you can point out that there are about 400,000 certified public accountants in the United States, according to the American Institute of Certified Public Accountants, and that 328,000 of these CPAs are members of the institute.

Look at the Bigger Picture

In researching the potential market for your book, consider all the populations to whom your book might be of interest or use. That inspirational book on living with diabetes naturally will be of interest to diabetics; who else would benefit from reading it? Doctors, nurses, and home health aides, for example, might be able to use it in their dealings with diabetic patients. Friends and relatives of diabetics might find it useful to understand what their loved one is coping with. Reporters who cover health issues might be able to use it in developing stories.

All of these potential markets should be included in your proposal. Quantify each of these markets as much as possible. For example, if you can find out how many doctors, nurses, and home health aides deal with diabetic patients, include that in your market discussion. Also include the source of your numbers, even if the numbers are only estimates: “The American Diabetes Association estimates that more than 18 million people suffer from diabetes, including more than 5 million people who are unaware they have the disease.”