I recently spent some time consulting on a project, which was in it's pre-production phase. While on site, I had the fun experience of watching a group of animators try to figure out how much disk space they were going to need for their film. Each time they ran the numbers they got a different answer!
It's actually pretty simple - figure out the size of a pixel, mulitply by the resolution, multiple by the frame rate, multiply by 60, multiply by the duration in minutes, mulitply that by the number of passes, and then take that HUGE number, and start deviding it by 1024, until you get something sensible.
As you can see the problem isn't difficult, but it is long, and easy to make a mistake. It doesn't help that not all of these numbers are fixed, and in fact it's really usefull to be able to try some variations to see how much extra space some extra passes, or higher depth images would cost you.
Enter MovieSize! A really simple iPhone app to calculate the size of your movie. Just dial in the settings and it tells you how much disk space you need. Hit the results button, and it'll give more info on number of files and such.
NCCA, Bournemouth University