Unless selecting a vari-focal camera (with an adjustable lens) It is important to select the correct camera lens option for where the camera is to be positioned. A smaller lens will give you a wider angle but will be "zoomed out more", while a bigger lens will narrow the angle down and "zoom in more". See below to give you some idea on angles of Megapixel HD Cameras:

The amount of hard drive space you require is dictated by how many cameras, as well as their resolution, frame rate settings, and whether you have H.265 encoding enabled or not to save space (We advise turning it on to double the capacity shown below with ease). 

Finally, you can often make your storage space last a lot longer by enabling motion-detected recording rather than continuous, especially if there are long periods of no activity (to perhaps double or more these figures again).

As a rule of thumb, we recommend 2 Terabytes for a 4 x 4/5MP HD camera setup, as this should give you approx 2 weeks using H.265 @ 20fps and that is on continuous, not motion-detected recording.

(You may only require the full 25 frames per second on certain cameras if things are fast-moving - ie above a till)

You can also use the Hikvision online calculator to work out what works best for you specifically: https://tools.hikvision.com/ca... 

(All of our hard drives come fitted and are CCTV-specific from one of the major brands)