1 good quality movie can use as much as 1 GB of data to download and or could even be 2 GB if it's a really good quality movie that you're downloading.
So expect to use at least 1 GB of data when downloading a movie which isn't a problem on unlimited internet but is on limited internet such as 4 G or satellite internet if you download a lot of movies.
Downloading 1 GB of data for a movie can take an hour or more to download depending on your internet connection speed.