1. Define why footage is retained
Start with how late an incident might be discovered. Add a margin to that delay instead of choosing an arbitrary long period.
2. Use average bitrate, not resolution alone
Two cameras at the same resolution can write very different amounts because of frame rate, codec, scene complexity, and quality settings. Read the average Mbps from the camera or NVR.
3. Separate continuous and motion recording
Motion savings vary with traffic, trees, rain, and sensitivity. Calculate continuous recording first, then measure a representative week.
4. Leave operating headroom
Allow roughly 10–20% for bitrate spikes, indexes, and formatting differences. This is planning margin, not a universal guarantee.
5. Correct the estimate with measured growth
Record storage growth over seven days, calculate the daily average, and multiply by the target retention. Include nights and bad weather when they matter.
6. Plan how to preserve an incident
Important footage should be exported promptly to another device. A rolling NVR volume can overwrite the event you intended to keep.
Sources and official tools
- AXIS Site Designer — official system design tool