How Many Days Does a 4 TB or 8 TB NVR Record? Table for 8–64 Cameras
A 4 TB NVR records about 5.7 days for 16 cameras at 4 MP H.265, continuous, 25 fps, using Hikvision's recommended 4,096 Kbps per camera (checked 14 Oct 2026). An 8 TB disk doubles that to 11.3 days. Switching to H.264 halves it; motion-only recording at an assumed 40% activity multiplies it by 2.5.
Last checked: 14 Oct 2026
The formula is fixed: days = disk bytes ÷ (cameras × bitrate × 86,400 s ÷ 8). Everything else on this page is that formula with a published bitrate plugged in. If your NVR records at a lower bitrate than Hikvision's sheet, you get more days, but you can only know that by reading the bitrate setting on your own recorder.
Verified against
- Hikvision, H.264(5) & H.264(5)+ Recommended Bit Rate at General Resolutions (FAQ PDF, 4 pages; hikvision.com). Gives the per-resolution bitrates used below.
- Hikvision, What's H.265+? (hikvision.com). Source for the 32.4% average-bitrate claim.
- Hikvision DS-7616NI-K2/16P and DS-7732NI-K4/16P product specifications (DS-7616NI-K2/16P, DS-7732NI-K4/16P). Both are marked "Discontinued" on the page, and they are used here only as examples of typical limits.
- Western Digital, WD Purple product page (westerndigital.com) and WD Purple product brief PB_WD_Purple_HDD (2024-01) (PDF). Source for the TB definition and the 180 TB/year workload rating.
- Checked 14 Oct 2026.
Recording days: 4 TB and 8 TB, continuous, 25 fps
Assumptions: 25 fps (India uses the 50 Hz/PAL frame family). Bitrates come from the Hikvision sheet, where the 25 fps value equals the 30 fps value. 1 Kbps = 1,000 bit/s. Disk sizes are decimal: "4 TB" = 4 trillion bytes, the definition WD states. No file-system overhead is deducted. The full grid is in the CSV (48 rows).
| Resolution / codec | Bitrate per camera (Kbps) | GB/day per camera | 4 TB: 8 cams (days) | 4 TB: 16 cams (days) | 4 TB: 32 cams (days) | 4 TB: 64 cams (days) | 8 TB: 8 cams (days) | 8 TB: 16 cams (days) | 8 TB: 32 cams (days) | 8 TB: 64 cams (days) |
|---|---|---|---|---|---|---|---|---|---|---|
| 2 MP H.265 | 2,048 | 22.1 | 22.6 | 11.3 | 5.7 | 2.8 | 45.2 | 22.6 | 11.3 | 5.7 |
| 2 MP H.264 | 4,096 | 44.2 | 11.3 | 5.7 | 2.8 | 1.4 | 22.6 | 11.3 | 5.7 | 2.8 |
| 4 MP H.265 | 4,096 | 44.2 | 11.3 | 5.7 | 2.8 | 1.4 | 22.6 | 11.3 | 5.7 | 2.8 |
| 4 MP H.264 | 8,192 | 88.5 | 5.7 | 2.8 | 1.4 | 0.7 | 11.3 | 5.7 | 2.8 | 1.4 |
| 8 MP H.265 | 8,192 | 88.5 | 5.7 | 2.8 | 1.4 | 0.7 | 11.3 | 5.7 | 2.8 | 1.4 |
| 8 MP H.264 | 16,384 | 176.9 | 2.8 | 1.4 | 0.7 | 0.4 | 5.7 | 2.8 | 1.4 | 0.7 |
Source for every bitrate: the Hikvision recommended bit rate sheet (1080P, 4MP 2560×1440 and 3840×2160 rows, 25 fps column). The sheet itself says to raise the bitrate by 20–30% "if the real environment is more complex", which cuts the days by a further 17–23%.
Two shortcuts make the table easy to read. Per that sheet, H.265 needs half the H.264 bitrate at 1080P, 4MP and 3840×2160 (not at every row: at 4CIF and below the ratio is smaller), so in the table 4 MP H.265 and 2 MP H.264 record for the same number of days. Per the same sheet, the 15 fps bitrate is half the 25 fps value (4 MP H.265: 2,048 vs 4,096 Kbps), so dropping to 15 fps doubles every number above.
Motion recording and smart codecs
No vendor publishes a figure for how much of the day a factory floor is in motion, so the 40% below is our assumption. It roughly covers one long shift plus loading and cleaning. Pre- and post-record time adds to it. Motion days = continuous days ÷ motion fraction.
| 4 MP H.265, 4,096 Kbps | 4 TB continuous (days) | 4 TB motion, 40% assumed (days) | 8 TB continuous (days) | 8 TB motion, 40% assumed (days) |
|---|---|---|---|---|
| 8 cameras | 11.3 | 28.3 | 22.6 | 56.5 |
| 16 cameras | 5.7 | 14.1 | 11.3 | 28.3 |
| 32 cameras | 2.8 | 7.1 | 5.7 | 14.1 |
| 64 cameras | 1.4 | 3.5 | 2.8 | 7.1 |
For smart codecs, the Hikvision H.265+ sheet gives a "target bitrate" of 2,048 Kbps for 4 MP at 25 fps, against a 4,096 Kbps maximum. That doubles the days, but only if the scene is calm.
Hikvision says H.265+ uses "about 32.4% of the bitrate of H.265 on average", per its white paper as quoted on its H.265+ page. The same page says the codec is tuned for scenes where background "rarely changes" and moving objects "appear only occasionally".
A working press line, a conveyor or a rotating spindle is the opposite of that scene. Don't size disk on a smart-codec saving you have not seen in the recorder's own fill rate.
Where brands differ
- Bitrate defaults differ between brands and firmware. The table uses Hikvision's sheet because it is the only brand sheet checked here that publishes a full resolution × codec × frame-rate grid. An equivalent official Dahua or CP Plus sheet was not found in web searches for this page (checked 14 Oct 2026); Dahua shows a "recommended" range in its camera UI.
- "Kbps" may mean 1,000 or 1,024 bit/s. Vendors don't say which. Treating it as 1,024 cuts every number above by about 2.3%.
- Displayed capacity is smaller than the label. 4 × 10¹² bytes is 3.64 TiB, and 8 TB is 7.28 TiB. An NVR that reports in binary units shows the smaller number, though the number of days doesn't change.
Two checks before you trust any day count
1. Can the NVR take the bitrate? Per its specification page, the 16-channel Hikvision DS-7616NI-K2/16P accepts 160 Mbps incoming, with 2 SATA bays of up to 16 TB each. The 32-channel DS-7732NI-K4/16P accepts 256 Mbps, with 4 SATA bays of up to 16 TB each.
| Cameras × profile | Total incoming (Mbps) | Fits 160 Mbps (16-ch example) | Fits 256 Mbps (32-ch example) |
|---|---|---|---|
| 16 × 4 MP H.265 | 65.5 | Yes | Yes |
| 16 × 8 MP H.264 | 262.1 | No | No |
| 32 × 4 MP H.265 | 131.1 | n/a (16-ch) | Yes |
| 32 × 8 MP H.265 | 262.1 | n/a | No |
If the total is over the limit, the recorder will either refuse the stream or you will have to lower the bitrate. Either way, the days in the table no longer apply.
2. Can the drive take the writes? Western Digital rates WD Purple (1–8 TB, product brief 2024-01) at "up to 180TB/year" workload, counting data written and read. Sixteen 4 MP H.265 cameras writing 65.5 Mbps around the clock put about 258 TB/year on the disk set. Spread across two drives that is about 129 TB/year each. On one drive it exceeds the rating.
What breaks in a factory
- Busy scenes and 50 Hz lighting raise the bitrate. Moving machinery, dust and LED flicker all make the encoder work harder, which shortens the days. Flicker fixes are covered in CCTV flicker under LED lights.
- Power cuts lose days, not minutes. A disk that comes back "uninitialized" can take the whole retention window with it. See NVR HDD uninitialized after a power cut before formatting anything.
- Heat matters. Both Hikvision recorders above list a working range of −10 °C to 55 °C. A panel next to a furnace or on a tin-roof mezzanine can exceed that.
- Substreams and AI. If an analytics box also pulls streams, it uses network capacity but not recording disk, unless the NVR records the substream too. See substream settings for AI analytics.
When to call the installer / what to ask the vendor
- Ask for the bitrate, frame rate and codec actually set on each channel, not the camera's maximum.
- Ask for the oldest recording date on the NVR today. That is your real retention, and you can compare it with the table.
- Ask whether the retention you need is set by an audit or a policy. See how long a factory must keep CCTV footage. For the TB needed for a target number of days, use the CCTV storage calculator.
Where Mama fits
Mama reads a factory's existing cameras over RTSP/ONVIF and tells the owner, in plain language, where machines stood idle and hours were lost. That works on the cameras and NVR already installed, whatever their retention. Leave an email or phone in the form below.
FAQ
How many days will a 4 TB hard disk record CCTV? It depends on camera count and bitrate. Using Hikvision's recommended bitrates at 25 fps, continuous recording on 4 TB lasts 22.6 days for 8 × 2 MP H.265 cameras and 5.7 days for 16 × 4 MP H.265. For 16 × 8 MP H.264 it lasts 1.4 days.
How long will an 8 TB NVR record 16 cameras? For 4 MP H.265 at 4,096 Kbps, continuous, it records about 11.3 days. With motion-only recording at an assumed 40% activity it records about 28 days. At 15 fps it records about 22.6 days.
Does H.265 double recording time over H.264? At Hikvision's recommended settings, yes, for 1080P, 4MP and 4K: the sheet's H.265 bitrate is exactly half the H.264 bitrate at those resolutions, so the days double. At small resolutions such as 4CIF the sheet's saving is less than half. Both the camera and the NVR must support H.265 for this to apply.