How Many Words to Write a Book?

Singapore
November 30, 2008 1:09pm CST
I would very much like to write a book, but have absolutely no idea how long it should be. What do you think is the average length of a paperback self-help book? If you have other experience in writing a book, can you tell me how many words it takes for you to write them? And tell me whether it is fiction or non-fiction and the genre you are writing. If you are intending to write a book soon, how many words are you targeting? Thank you for your response!