The useful calculation
For continuous recording, approximate GB per day = total average bitrate in megabits per second × 10.8. Divide usable storage in decimal GB by that daily amount to estimate days. Four cameras averaging 4 Mb/s each total 16 Mb/s: 16 × 10.8 = 172.8 GB/day. A nominal 2 TB treated as 2,000 GB gives a theoretical 11.6 days before allowing for unavailable capacity and other recording overheads.
Try a continuous-recording estimate
Continuous recording, decimal storage units. This planning tool uses a constant average bitrate and does not guarantee installed retention.
At 16 Mb/s total: approximately 172.8 GB per day and 11.6 theoretical days from 2,000 GB.
Use actual usable space where known. Allow for recording overheads and verify real playback history after installation.
Worked examples at constant average bitrate
| Example | Data per day | Theoretical days from 2,000 GB |
|---|---|---|
| 4 cameras × 2 Mb/s = 8 Mb/s total | 86.4 GB | 23.1 days |
| 4 cameras × 4 Mb/s = 16 Mb/s total | 172.8 GB | 11.6 days |
| 8 cameras × 4 Mb/s = 32 Mb/s total | 345.6 GB | 5.8 days |
Why the installed result can differ
A drive label is not the same as usable recording capacity. Variable bitrate, activity, frame rate, audio, stream configuration and recorder storage policies can change consumption. Motion/event-only recording cannot be reduced reliably to an arbitrary percentage of a day without evidence of actual activity. Treat the arithmetic as a planning comparison, then verify the installed timeline.
What to request in the CCTV quote
- Number of recording streams and the intended resolution/frame/encoding settings.
- A realistic bitrate or measured storage assumption for those settings.
- Usable storage and the required retention target, stated separately from nominal drive size.
- A post-installation check of the actual timeline and a successful clip export.
Questions and answers
Can I promise a fixed number of days from drive size alone?
No. Drive capacity without the camera recording settings and actual workload is insufficient. Ask for the estimate’s assumptions and verify the installed result.
Does reducing the bitrate always improve the design?
It may extend storage at the expense of useful image detail. Evaluate recorded movement in the target scene and agree the evidence requirement before trading image quality for retention.
Sources and equipment references
Checked for the product, supplier or information details used here. Exact procedures depend on the installed model; these links are not a substitute for its instructions.