How do I determine amount of recording time?

Is there a general formula for determining the amount of recording time for a camera setup? For example, if you have 4 cameras running 24/7 all day and night at 15fps, how large of a drive would you need to record 7 continuous days? Thanks.

that depends on the DVR you are using, Compression used, and what Resolution the DVR is set to/capable of recording at.

Here is a storage calculator. There are lots of them out there on the internet. This one needs to know the "average image size" and the specs of a DVR might mention that but you should be able to get that info from the manufacturer.

http://www.luxriot.com/calcstorage.html

Your storage requirements will also be greatly affected by the type of camera you use. The complexity of the scene. And the amount of light.

Thats right, high quality color images will take up alot more space than BW images, this makes a huge difference especially when recording in highest resolution and real time..

And crappy colored images will even take up more space due to the excess noise in the video.