CCTV storage calculator
How many terabytes you need for the retention you want. Bitrates are typical figures, not a guarantee: a busy scene with lots of movement always uses more than a quiet one.
Storage needed
Add headroom: drives are sold in decimal terabytes and a recorder should not run full. Many installers size 20–30% above the calculated figure, and RAID or a spare drive changes the total again.
The arithmetic
Storage is just bitrate times time. One megabit per second uses about 0.45 GB an hour, so a 4MP camera at around 3 Mbps uses roughly 32 GB a day, and eight of them for thirty days is a bit over 7 TB.
The variables that move the number most are resolution, frame rate and whether the scene is busy. A camera watching a still corridor compresses far better than one pointed at a windy car park with trees. Full detail is in the storage and retention guide, and the network guide covers what those bitrates mean for your switch and internet connection.