Why isn't the number of cameras enough?
Two cameras at the same resolution can consume very different capacities because of their bitrate, frame rate, encoding, and how much motion is in the scene. That is why "a 4 TB drive is enough" is never accurate until the recording settings are known.
The four factors in the calculation
The calculation starts from each camera's actual bitrate, then multiplies by the number of cameras, the recording hours per day, and the number of days — plus an operational margin. Continuous recording differs from motion-triggered recording, but sites under regulatory requirements should not lean on unapproved assumptions just to shrink the capacity.
What the calculation is built from
- Number of cameras
- Bitrate per camera (Mbps)
- Retention period
- Capacity margin and disk continuity
30 days or 90 days?
The final retention period is tied to the site's classification and the supervising authority. Financial institutions, for example, carry their own requirements, while other sites may be classified as low or medium sensitivity. The advisor calculates a preliminary capacity, then asks you to confirm the classification before the quote is finalized.
Frequently asked questions
Does H.265 reduce storage?
Usually yes — but the result depends on the scene, the quality setting, and whether both the camera and the recorder actually support it.
Can capacity be calculated without a site survey?
A preliminary estimate is possible, but the final sizing needs the real bitrate settings and the actual retention period.
Practical takeaways
- Ask for the disk capacity to be calculated on your cameras and settings, not quoted as "enough"
- Fix the retention period first — 30 or 90 days changes everything downstream
- Confirm the site classification before the capacity is locked in
- Keep an operational margin so the disk doesn't overwrite footage early
- Enable smart encoding (H.265) where the camera and recorder both support it