Shooting ratio is simply the ratio between the amount of footage you shoot, and the length of the finished film. For example, if you shoot 60 hours of footage, total (including all the takes) for a 90-minute feature, then your shooting ratio is 60/1.5 = 40 to 1.
This is simple enough; but figuring out, in advance, what your shooting ratio will be for a particular project can be very hard. Real-life shooting ratios are all over the place, from 1:1 (Primer) to 300:1 (Deadpool). A typical amateur drama might have a shooting ratio anywhere between 10:1 and 50:1. So how can you figure out what yours will be?
Only you can know what you plan to shoot, and how. If you're going to rehearse heavily, and then shoot only when everyone is very ready, and with minimal coverage, then your ratio could be low — 5:1, 3:1, or even, like Primer, close to 1:1.
If, on the other hand, you use the cheapness of video to shoot more spontaneously, then your ratio will be high: 50:1, 100:1, or even 200:1 (like Gone Girl). But bear in mind that a high shooting ratio will have a real cost: not only will you need more data storage, and spend more time uploading and copying data; but your editor will have to wade through all those rushes, and categorise and rate everything before they can even start editing.
Documentaries can be absolutely anywhere, depending on the subject. For example, if your documentary is about bald eagles, and you plan to have a camera on the nest every second for a year, then you will have close to 9,000 hours of footage — per camera. For a 90-minute documentary, that's a 6,000:1 ratio right there.
So only you can have any idea what your shooting ratio will be. Think about exactly what you plan to shoot, and how you plan to shoot it, and make the best guess you can. Once you have an idea, you can put it into the data calculator and see what effect it has.
One thing's for sure, guess high and leave plenty of margin for error, because you will probably end up shooting way more than you planned. If not, then well done!
