By the SightShield team · · 3 min read
Channels are only the first number
NVRs are sold by channel count — 4, 8, 16, 32, 64 — which is the number of cameras they can record. But two NVRs with the same channel count can behave very differently with your cameras. Incoming bandwidth, decoding power and disk capacity decide whether a 16-channel NVR can really handle sixteen 4MP or 8MP cameras recording at full quality.
Specifications that matter
| Spec | What it means | What to check |
|---|---|---|
| Channels | Maximum number of cameras | Leave spare channels for growth |
| Incoming bandwidth | Total Mbps of video the NVR can receive and record | Must exceed the sum of all camera bitrates |
| Decoding capacity | How many streams it can display or play back at once | Matters for multi-camera live view and playback |
| HDD bays and max per bay | How much storage fits inside | Enough for your retention days |
| Built-in PoE ports | Power and connect cameras directly | Convenient for small sites; check PoE budget |
| AI features | Human/vehicle detection, face, smart search | Number of AI channels supported |
| RAID | Disk redundancy if one fails | Useful for 32+ channels and critical sites |
| Video outputs | HDMI/VGA, 4K, dual output | Matches your monitor plan |
Working out bandwidth
Add up the bitrate of all cameras. With H.265, a 4MP camera at good quality typically uses around 4 Mbps and an 8MP camera around 8 Mbps, though settings vary. Sixteen 4MP cameras need roughly 64 Mbps; thirty-two 8MP cameras need about 256 Mbps. Choose an NVR whose incoming bandwidth comfortably exceeds your total, with headroom for higher bitrates at night or in busy scenes.
H.265 vs H.264 compression →Sizing examples
| Site | Cameras | Typical NVR |
|---|---|---|
| Flat or small shop | 2–4 × 4MP | 4- or 8-channel with built-in PoE, 1 HDD bay |
| Villa or office floor | 8–12 × 4MP | 16-channel, 2 HDD bays, some AI channels |
| Large office or apartment block | 20–32 mixed 4MP/8MP | 32-channel, 4 HDD bays, 256 Mbps+, 4K output |
| Factory or campus | 64+ | 64-channel NVRs with RAID, or several NVRs under a VMS |
Storage and retention
A useful rule of thumb is about 20 GB per 4MP camera per day of continuous recording. Sixteen 4MP cameras for 30 days need roughly 10 TB, which means two or more disks. Check the NVR’s maximum capacity per bay and use surveillance-grade disks.
CCTV hard disk size calculator →Built-in PoE or separate switch?
NVRs with built-in PoE ports are neat for small systems where all cameras are within cable range of the recorder. For larger sites, or where cameras are spread across floors and buildings, separate PoE switches near the cameras are better, connected to the NVR over the network.
Choosing a PoE switch for CCTV →Matching brands
- Same-brand cameras and NVR give full AI features, easy setup and one app.
- ONVIF allows mixing brands, but AI events and some settings may not pass through.
- Check that the NVR model, like the cameras, is acceptable under India’s certification rules for your purchase.
Common mistakes
- Buying exactly as many channels as cameras, with no room to add more.
- Ignoring incoming bandwidth when upgrading to 8MP cameras.
- Too few disk bays for the retention needed.
- Placing the NVR in a hot, unventilated cupboard.
Get the right size
We size the NVR from your camera list, bitrates and retention days, leaving room for growth.
CCTV installation →Quick answers
How many cameras can one NVR handle?+
Up to its channel count, provided the total camera bitrate is within its incoming bandwidth and decoding limits.
Which NVR do I need for 16 cameras?+
A 16-channel NVR fits exactly; a 32-channel model leaves room to grow. Check bandwidth and disk bays for your retention.
Can I mix camera brands on one NVR?+
Often via ONVIF, but AI features may not work across brands.
Do I need RAID?+
For large or critical systems, RAID protects recordings if a disk fails.
What is incoming bandwidth on an NVR?+
The total video data the NVR can receive and record from all cameras, in Mbps.