How many days of video do you want to store?  
Number of cameras recording?   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Number of frames per second you would like each camera to record?   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
How many hours per day does the facility operate?   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
How many days of the week does the facility operate?    1 2 3 4 5 6 7  
You will need about of hard drive space to meet your storage needs.

 Tips:

• 1 frame per second is the lowest frame rate recordable and 30 frames per second is the maximum which is real time
• There is no real need to record in real time unless there are regulatory reasons as in case of government facilities or casinos
• Recording at 1 frame per second is what traditional analog systems record
• You can always rewind in high speed so the lower the frame rate the faster it is to playback an entire day
• At 3 - 5 frames per second recording you will not miss any activity (remember this is per second)