CCTV Storage Sizing: Retention, Resolution and Real-World Bitrate

The basic calculation

For a camera recording continuously, storage per day is its average bitrate multiplied by the seconds in a day. One megabit per second equals 450 MB per hour, or about 10.8 GB per day. Multiply by the number of days to keep and the number of cameras, then add overhead.

An illustration, not a benchmark:

Then convert usable capacity into the number of drives needed for the RAID level or erasure coding scheme, remembering that a drive sold as 8 TB shows about 7.3 TiB in most operating systems.

Purpose decides resolution

Before choosing cameras, agree what each view must achieve. IEC 62676-4 describes pixel density levels for detecting, observing, recognizing and identifying people: roughly 25, 62.5, 125 and 250 pixels per meter at the target. A camera meant to identify faces at an entrance needs far more pixels on the target than one that detects movement along a fence. Higher resolution and frame rate raise bitrate, so over-specifying every camera wastes storage.

What changes bitrate

• Resolution and frame rate.
• Codec: H.265 usually needs less bitrate than H.264 for similar quality; vendor "smart" codecs can reduce it further in static scenes.
• Quality settings and whether bitrate is constant or variable.
• Scene complexity: moving trees, traffic, crowds and flickering lights.
• Lighting: low light and infrared scenes add noise, which encoders treat as detail.

Measure instead of guessing

1. Install sample cameras in representative positions, or use existing cameras with the planned settings.
2. Record for at least a full day and night, including busy periods.
3. Read average and peak bitrates per camera from the recorder or video management system.
4. Use per-scene averages in the calculation, and plan for the busiest realistic conditions.

Recording modes and retention strategies

• Continuous recording is simplest and never misses an event, at the highest storage cost.
• Motion or event recording saves storage in quiet areas but depends on reliable detection; poorly tuned rules miss events or record all the time.
• Dual streams record a high-quality stream and use a lighter stream for live viewing.
• Tiered retention keeps full frame rate for recent days and reduces older footage, where the platform supports it.

Choosing retention

Retention should follow purpose. Consider how long incidents typically take to be reported, such as stock losses found at month-end counts, plus any legal, contractual or insurance requirements. Video of identifiable people is personal information under the Data Privacy Act. The National Privacy Commission's Circular No. 2024-02 on CCTV systems sets no fixed retention period: footage may be kept only as long as necessary for the purpose it was collected for, the retention period must be documented in the CCTV policy, footage must be destroyed once it is no longer needed, and retention must not be decided based solely on the storage capacity of the system. Size storage for the retention you have justified, not the other way around.

Storage architecture

• Use RAID 6 or erasure coding for large arrays so they survive two drive failures during a rebuild.
• Choose drives rated for continuous surveillance workloads, and keep hot spares.
• Add failover recording servers for larger systems.
• Consider camera-side storage as a buffer during network interruptions.
• Size the camera network for the combined bitrate of all streams.

Verify and monitor

• After the retention period has passed, confirm that the oldest recording on each camera meets the target.
• Alert on drive failures, recording gaps, cameras offline and storage filling faster than planned.
• Re-measure bitrates when cameras, settings or scenes change.