Beginning Writer’s Answer Book by Jane Friedman
Should I send a synopsis with my query letter? If so, how long should it be?
If editors or agents request a synopsis with your query, they’re probably looking for a quick summary of your entire novel. Synopsis lengths vary, but one to three pages is typical if no length is stipulated. Sometimes agents or editors ask for an outline, which is often used interchangeably with the word "synopsis." Or, when asking for an outline, an agent/editor may want a chapter-by-chapter outline (a synopsis of each chapter). When in doubt, ask.