The two are very different.
Let’s start at a basic level. The action in screenplays is always in the present tense, while the most common tense used in novel narratives is the simple past tense. This alone can drive you a little nuts when switching between novels and screenplays. Whatever tense you’re currently writing in becomes habitual; it feels natural and intuitive. You do it without thinking. And worse, unless you deliberately read for tense, you simply won’t catch all the times when you’ve incorrectly got past tense in the screenplay action or present tense in the novel narrative. And, strangely, when you make the change, at first it feels wrong somehow.
The number of words you have to play with in a screenplay is far less than what you have at your disposal in a novel. My screenplay for Conquist is around 22,000 words while my novel version is 86,000 words. In fact, the movie industry doesn’t even talk about the number of words. It talks about pages. The average movie screenplay is around 110 pages, which are formatted in such a way that a page represents around one minute of screen time. So, the 110 pages represent just under two hours, which is somewhere near the average length of a movie. You need to be aware, though, that this restriction on the number of pages only really applies to spec scripts—that is, the ones that are written on-spec without a contract. If you’re Tarantino, you can go for broke.
And if you think manuscript requirements for novels or short stories are over-prescriptive, you ain’t seen nothing yet. The formatting requirements of screenplays appear overwhelming at first. I don’t know how they managed it in the Golden Age of Hollywood, but I wouldn’t even think of writing a screenplay without a software package like Final Draft.
This blog appeared in a different form as an Editorial in Aurealis #124.