Related tools
Need to size the HDD instead? Use the CCTV Storage Calculator. Choosing NVR drives? Find a practical HDD configuration. Planning the network too? Calculate IP camera bandwidth.
How CCTV Recording Time Is Calculated
Recording time is available storage divided by planned daily recording consumption. Daily consumption depends on configured bitrate, number of cameras, recording hours per day, and storage overhead.
Total storage bytes = storage TB x 1,000,000,000,000
Base bytes/day = bitrate bits/sec x recording seconds/day x cameras / 8
Planned bytes/day = base bytes/day x (1 + overhead percentage / 100)
Recording days = total storage bytes / planned bytes/day
Why Bitrate Matters More Than Resolution Alone
Two cameras with the same resolution can use different storage because frame rate, image quality, codec, scene complexity, CBR/VBR settings, and camera configuration all affect the recorded bitrate.
H.264 vs H.265
H.265 can often achieve lower bitrate than H.264 at comparable image quality and configuration, but there is no guaranteed universal percentage. The calculator therefore uses the bitrate entered by the user.
Continuous vs Scheduled Recording
24 hours per day represents continuous recording. Lower values can represent a known schedule, such as cameras that record only during business hours.
Motion Recording
Motion or event recording may increase retention because cameras are not recording continuously, but exact recording time cannot be predicted without knowing real activity. An empty warehouse, busy shop, street, and parking area can produce very different active recording time.
CBR vs VBR and Retention Time
CBR aims around a configured bitrate. VBR can vary more depending on scene complexity and activity, so actual retention may differ from the estimate even when the settings look similar.
Why Actual HDD Recording Time Can Differ
Actual retention can change with average bitrate, VBR behavior, recorder database or file-system use, metadata, audio recording, camera configuration, event recordings, and reserved recorder space.
Example CCTV Recording Time Calculation
With 4 TB storage, 4 cameras, 4 Mbps per camera, 24 hours per day, and 10% overhead, base daily use is 172.8 GB. Planned daily use is 190.08 GB. Dividing 4,000 GB by 190.08 GB/day gives about 21.04 days.
FAQ
How long will a 1TB HDD record CCTV?
It depends on camera count, configured bitrate, recording hours, and overhead. A single low-bitrate camera can last much longer than many cameras recording continuously at high bitrate.
How long will a 4TB HDD record 4 cameras?
At 4 Mbps per camera, 24 hours per day, and 10% overhead, 4 TB provides about 21 days of recording. Different bitrates or schedules can change that substantially.
How many days can an 8TB NVR record?
The answer depends on the total daily recording consumption. Doubling storage doubles retention only when camera count, bitrate, recording hours, and overhead stay the same.
Does H.265 increase recording time?
H.265 can increase recording time if it lets you use a lower bitrate at comparable quality, but there is no guaranteed universal percentage. This calculator uses the bitrate you enter.
Does motion recording last longer than continuous recording?
Often it can, because cameras may record fewer hours, but exact retention depends on real activity in the scene. An empty warehouse and a busy shop can trigger very different recording amounts.
Does camera resolution determine recording time?
Resolution matters, but it does not determine recording time by itself. Frame rate, codec, image quality, scene complexity, CBR/VBR settings, and camera configuration all affect bitrate.
How does bitrate affect CCTV recording days?
Higher bitrate consumes more storage per hour, which reduces retention. Lower bitrate consumes less storage, but image quality and scene detail may also change.
How much recording time will I get from 8 cameras?
Use the configured bitrate and available storage. Eight cameras at the same bitrate use twice the daily storage of four cameras, so retention is roughly half if storage is unchanged.
Planning note
Treat this as a planning estimate. Verify real recorder behavior, average bitrate, reserved storage, and recording schedule before relying on a retention target.