How to calculate CCTV storage (with examples)
One of the most common mistakes in video surveillance projects is too little storage: the recorder overwrites old footage sooner than expected, and just when a recording is needed it no longer exists. Fortunately, the calculation is simple.
The basic formula
Recording size depends on the video bitrate (the amount of data per second), not directly on megapixels:
Daily size per camera (GB) = bitrate (Mbps) × 86,400 ÷ 8 ÷ 1000
86,400 is the number of seconds in a day, and dividing by 8 converts megabits to megabytes. Then multiply the result by the number of retention days and the number of cameras.
Example
Suppose 16 four-megapixel cameras using H.265 compression with an average bitrate of 4 Mbps record continuously, and footage must be kept for 30 days:
- Daily size per camera: 4 × 86,400 ÷ 8 ÷ 1000 = 43.2 GB
- For 30 days: 43.2 × 30 = about 1.3 TB per camera
- For 16 cameras: about 20.7 TB
With a safety margin of about 10 to 20 percent, a capacity of around 24 TB is appropriate.
What changes the bitrate?
- Compression: under similar conditions, H.265 usually needs a lower bitrate than H.264.
- Frame rate: recording at 15 frames per second instead of 25 or 30 noticeably reduces size and is enough for most security uses.
- Scene complexity: busy scenes, trees in the wind, rain or image noise at night all raise the bitrate.
- Motion-based recording: in low-traffic areas, recording only on motion can cut storage several times over.
A few recommendations
Use surveillance-grade hard drives for 24-hour recording. In critical projects, a RAID array or a separate storage server protects against a single drive failure. Check the real bitrate in the recorder settings after installation and update the calculation if needed.