I am not a writer. Well, I was (I have been writing business related documents and white papers for years) and wasn’t (as in an eBook or “real” book writer) until I committed to writing a book (actually at least two non-fiction books per year.)
Back to not being a writer. One of the issues I had to deal with was how long of a book to write. I needed a target to to have some sense of when I had what I would consider a book-length manuscript. I am not super prolific and believe strongly that most people do not need the 250-page non-fiction book. In fact, according to Kindle statistics, yes Amazon knows abut your reading habits, most people don’t finish their business books (see “Your E-Book is reading You” from the Wall Street Journal.) Frankly, I think that most non-fiction can be a bit word-padded (I just made that term up) to get to a marketable page count to satisfy traditional publishers. Once upon a time, I even thought that I would create a series of short books under a form of imprint related to attention deficit disorder. Imagine, “ADD Books.” Books for the millions of the unfocussed.
Back to length. There are no rules. However, research indicates that most fiction books seem to fall into the following range: Books are about 60,000 to 125,000 words or 200 to 500 pages at 250-350 words per page. Most fiction starts at about 80,000 words.
However, non-fiction books run the gamut and can be much smaller. My favorite non-fiction, especially for business books, tends to be punchier and designed to be quicker reads (think of Seth Godin.)
“Boomercide”, my non-fiction book, is topping out at about 20,000 words or 80 to 90 pages at 6”X9”. This works for me as the book is intended to be very direct. No fluff. I am trying to get to the point.
So, how long should a book be? Depends… as usual.