When asked how long a paper should be, an English professor I had in college would reply in his slow Virginia drawl, “A written work should be as long as a lady’s hemline. Long enough to cover the subject but short enough to keep it interesting.”
While his instruction might be seen as inappropriate in today’s classroom, I have never forgotten his words and still share them to help clients think through both the outline and edit of their books. However, when it comes to actual word count for a manuscript, there are norms authors should be aware of, especially if they are seeking a traditional publisher or agent:
In general, nonfiction books contain anywhere from 30,000 to 75,000 words.
Nonfiction academic and self-help books are usually at the higher end of that word count at 60,000 and above.
Nonfiction business books typically average from 35,000 to 55,000 words.
Memoirs, though nonfiction, gravitate toward the lower-range in word counts for fictional novels. Memoirs can be 75,000 to 90,000 words. But unless you are famous or have something earthshaking to reveal, it’s wise to keep a memoir closer to 75,000 words.
E-books can run between 3,000 and 25,000 words.
To give you an idea of how these word counts translate into book size: Using 12-point type, an average printed page holds from 250 to 300 words, depending on the font. So if we split the difference at 275 words per page, a 55,000-word business-book manuscript equals a 200-page printed book, give or take.
Remember, these numbers are only guidelines. Ultimately, you are the writer, and the word count is up to you.