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Quick answer: For 30 days of 24/7 recording on H.265 at 25 fps, plan around 11 TB for 16 × 2MP cameras, 23 TB for 16 × 4MP, 46 TB for 32 × 4MP, and 91 TB for 64 × 4MP cameras. These figures include an industry-standard buffer. Motion recording and smart codecs like H.265+ can bring them down by 40-60%.
Something goes missing from a warehouse. The owner asks for footage from three weeks back. The NVR has already overwritten it.
Nobody did anything “wrong” during installation. The drive was sized for 30 days of 1080p, then the client upgraded to 4MP cameras, and nobody redid the math. Retention quietly dropped to 13 days.
This guide gives you the formula, ready-made tables for 16, 32, and 64 camera projects, and the mistakes that cause this exact problem. If you’re a system integrator quoting a project, you can use the tables directly.
The NVR Storage Formula
There’s one formula behind every CCTV storage calculator:
Storage per camera per day (GB) = Bitrate (Mbps) × 10.8
Total storage (GB) = Storage per camera per day × Number of cameras × Retention days
Where does 10.8 come from? A camera streaming at 1 Mbps for 24 hours writes 86,400 megabits. Divide by 8 to get megabytes, then by 1,000 to get gigabytes, and you get 10.8 GB per day.
A quick worked example: 16 cameras at 4 Mbps for 30 days.
- 4 × 10.8 = 43.2 GB per camera per day
- 43.2 × 16 = 691 GB per day for the whole system
- 691 × 30 = 20,736 GB ≈ 20.7 TB
- Add a 10% buffer → about 23 TB
The whole calculation depends on the bitrate you start with. Get that wrong and everything after it is wrong too.
What Bitrate Should You Use?
Bitrate depends on resolution, codec, frame rate and how much movement the camera sees. A camera facing an empty corridor at night writes far less than one facing a busy shop floor or a highway.
For planning, we use these conservative numbers (25 fps, continuous recording, medium activity):
| Resolution | H.264 Bitrate | H.265 Bitrate | H.265 Storage per Camera per Day |
| 2MP (1080p) | 4 Mbps | 2 Mbps | 21.6 GB |
| 4MP | 8 Mbps | 4 Mbps | 43.2 GB |
| 8MP (4K) | 16 Mbps | 8 Mbps | 86.4 GB |
H.264 needs roughly double the storage of H.265 for the same picture quality. If your cameras support H.265, use it. There’s very little reason to record H.264 on a new project in 2026.
The best number, though, is the one actually set in the camera. Open the camera’s web interface and check the main stream bitrate. If it’s set to 6 Mbps, use 6 in the formula, not the table value.
Storage Tables for 16, 32 and 64 Cameras
All tables below assume H.265, 25 fps, continuous 24/7 recording, and the bitrates above. They show raw storage before buffer and RAID.
16 Cameras
| Resolution | Per Day | 30 Days | 60 Days | 90 Days |
| 2MP | 346 GB | 10.4 TB | 20.7 TB | 31.1 TB |
| 4MP | 691 GB | 20.7 TB | 41.5 TB | 62.2 TB |
| 8MP | 1.38 TB | 41.5 TB | 82.9 TB | 124.4 TB |
32 Cameras
| Resolution | Per Day | 30 Days | 60 Days | 90 Days |
| 2MP | 691 GB | 20.7 TB | 41.5 TB | 62.2 TB |
| 4MP | 1.38 TB | 41.5 TB | 82.9 TB | 124.4 TB |
| 8MP | 2.76 TB | 82.9 TB | 165.9 TB | 248.8 TB |
64 Cameras
| Resolution | Per Day | 30 Days | 60 Days | 90 Days |
| 2MP | 1.38 TB | 41.5 TB | 82.9 TB | 124.4 TB |
| 4MP | 2.76 TB | 82.9 TB | 165.9 TB | 248.8 TB |
| 8MP | 5.53 TB | 165.9 TB | 331.8 TB | 497.7 TB |
Practical HDD Configurations for 30-Day Retention
This is what we’d actually quote, with an industry-standard buffer added:
| System | Storage Needed (with buffer) | Suggested HDD Setup |
| 16 × 2MP | ~11.4 TB | 2 × 6 TB or 1 × 12 TB |
| 16 × 4MP | ~22.8 TB | 2 × 12 TB or 4 × 6 TB |
| 16 × 8MP | ~45.6 TB | 4 × 12 TB |
| 32 × 2MP | ~22.8 TB | 4 × 6 TB or 2 × 12 TB |
| 32 × 4MP | ~45.6 TB | 4 × 12 TB or 8 × 6 TB |
| 32 × 8MP | ~91.2 TB | 8 × 12 TB |
| 64 × 2MP | ~45.6 TB | 4 × 12 TB or 8 × 6 TB |
| 64 × 4MP | ~91.2 TB | 8 × 12 TB |
| 64 × 8MP | ~182.5 TB | 16 × 12 TB, or a VMS server with external storage |
Once you cross about 64 cameras at 4MP and above, a single NVR usually isn’t the right answer. A VMS platform such as Honeywell MAXPRO VMS, Videonetics, Digifort, Milestone or Network Optix, running on a server with dedicated storage, scales better and is easier to manage. Our CCTV and video surveillance distribution team can help you decide which setup fits a project.
How Much Do Motion Recording and H.265+ Really Save?
On paper, a lot. Motion-only recording and smart codecs (H.265+, Smart Codec, WiseStream, and similar) can cut storage by 40-70%.
In practice, it depends entirely on the scene. A server room camera that sees movement twice a day will save a huge amount. A camera covering a factory floor during three shifts, or a road with constant traffic, will save almost nothing.
Our position: size the storage for continuous recording, and treat smart codec savings as a bonus. If you size for motion recording and the client later moves a camera to a busy entrance, retention drops and nobody notices until the day they need old footage.
The one exception is a large project with a tight budget. There, you can mix: continuous recording on entrances, cash counters and loading bays, and motion recording on low-traffic areas. Just calculate each group separately and add them up.
Your 12 TB Drive Isn’t Really 12 TB
Hard drive makers count 1 TB as 1,000 GB. Operating systems and NVRs count it as 1,024 GB. So a 12 TB drive shows up as roughly 10.9 TB once installed, about 9% less than the label.
That’s one reason the 10% buffer in our tables matters. Skip it and your “30-day” system becomes a 27-day system on day one.
RAID: When Is It Worth It?
RAID protects footage when a drive fails, but it costs capacity.
| RAID Level | Capacity Lost | Survives | Good For |
| No RAID | None | No drive failure (only that drive’s footage is lost) | Small systems, up to ~16 cameras |
| RAID 1 | 50% | 1 drive failure | 2-bay NVRs where footage is critical |
| RAID 5 | 1 drive | 1 drive failure | 32-camera systems, 4+ drives |
| RAID 6 | 2 drives | 2 drive failures | 64+ cameras, banks, jewellery showrooms |
Example: 8 × 12 TB in RAID 6 gives you 72 TB usable, not 96 TB. Always calculate RAID loss after you’ve worked out the storage you need, then add drives to cover it.
For 64-camera projects, we also recommend a hot spare: one extra drive sitting in the NVR that automatically replaces a failed one.
Use Surveillance HDDs, Not Desktop Drives
A desktop hard drive is designed for a few hours of use a day, mostly reading. An NVR writes video 24 hours a day, 365 days a year, from many cameras at once.
Surveillance drives like WD Purple and Seagate SkyHawk are built for this workload. They’re rated for far higher yearly data writes and use firmware tuned for multiple video streams. For enterprise systems, the higher-tier versions such as WD Purple Pro handle heavier workloads and larger NVR arrays.
We’ve seen desktop drives fail within a year in NVRs. And in India, two more things shorten drive life:
- Heat. An NVR sitting in a closed electrical room in an Ahmedabad summer can easily run above 40°C. Drives at that temperature fail faster. Make sure the NVR has ventilation, or put it in an air-conditioned rack.
- Power cuts. Sudden power loss while writing can corrupt drives and recordings. A UPS for the NVR and PoE switch is not optional.
Check Your NVR’s Limits Before Buying Drives
Storage math is only half the job. The NVR also has hard limits:
- Number of HDD bays: A 2-bay NVR can’t hold 4 drives, no matter what your calculation says.
- Maximum capacity per bay: Many NVRs support 10, 12 or 16 TB per bay. Check the datasheet before quoting 16 TB drives.
- Incoming bandwidth: This is the one people forget. If a 32-channel NVR supports 256 Mbps incoming bandwidth, and you connect 32 × 8MP cameras at 8 Mbps each, you’re at exactly 256 Mbps. There’s no headroom. Either choose a higher-bandwidth NVR or lower the bitrate.
- Network capacity:. The switch uplink to the NVR must carry the total bitrate of all cameras. For bigger projects, a gigabit uplink or fibre backbone is a must. See our active and passive networking range for PoE switches built for surveillance traffic.
4 Storage Sizing Mistakes We See Often
Using the sub-stream bitrate. New generation cameras can send 3 and 4 streams as well: a high-quality main stream for recording and a low-quality sub-stream for mobile viewing. Calculating storage from the sub-stream (often 512 Kbps–1 Mbps) gives a number 4–8 times too small.
Not recalculating after a resolution upgrade. The project was quoted with 2MP cameras. The client upgraded to 4MP at the last moment. The cameras changed, the drives didn’t, and retention halved.
No room for expansion. Most sites add cameras within two years. Add 20–25% extra capacity, or at least choose an NVR with free bays so drives can be added later.
Promising retention without checking it. If your contract says 30 days, check the oldest recording on the NVR a month after handover. It takes two minutes and protects you if there’s ever a dispute.
Planning Storage for a Project?
ADI Solutions supplies IP cameras, NVRs, VMS software, surveillance-grade hard drives and networking hardware to system integrators and dealers across Gujarat, Maharashtra and Rajasthan. Send us your camera count, resolution and retention requirement, and we’ll recommend the right NVR and HDD configuration.
Get a project quote from ADI Solutions →
Frequently Asked Questions
How much storage do I need for 16 CCTV cameras?
For 30 days of continuous H.265 recording, 16 × 2MP cameras need about 11 TB and 16 × 4MP cameras need about 23 TB, including a 10% buffer. For 4K (8MP) cameras, plan around 46 TB.
How many days will a 4 TB hard disk record?
With 8 × 2MP cameras on H.265 recording 24/7, a 4 TB drive lasts about 3 weeks. With 4 cameras, it lasts around 6 weeks. With 4MP cameras, those numbers roughly halve.
Can I use a normal hard disk in an NVR?
It will work, but it won’t last. Desktop drives aren’t built for 24/7 multi-stream writing. Use surveillance-grade drives like WD Purple or Seagate SkyHawk.
How long should CCTV footage be stored in India?
Thirty days is the most common requirement for commercial sites, and many police and state public-safety notifications ask covered establishments to keep about that much. Banks, jewellery showrooms and some industrial sites often keep 60–90 days. Check the exact rule for your client’s city and business type before finalising storage.
Disclaimer: The storage calculations in this article are based on general industry estimates. Actual available storage and performance may vary depending on your system configuration, operating system overhead and the compression methods used by different OEMs (Original Equipment Manufacturers). For an exact sizing, check the camera and NVR datasheets or contact our team.