How-To
What Size NVR Do I Need? Channels, Bandwidth and Storage
How-ToCount the cameras, buy that many channels. That’s how most people size a recorder, and it mostly works. Right up until the day it doesn’t, which is usually about six months later, when someone adds two cameras to the yard and the whole thing starts dropping frames at three in the morning.
Channels are the easy bit. What actually decides whether a recorder copes sits further down the datasheet, in among the numbers nobody bothers printing on the box, and those are exactly the ones that get skipped.
Bandwidth
An eight-channel NVR at the budget end might cap incoming bandwidth at 80 Mbps. Sounds like plenty. Then you hang eight 4K cameras off it at a decent bitrate, and eight 4K streams running 24/7 colour can ask for 112 Mbps between them. The recorder will not warn you about this. It just starts dropping frames. Or it quietly refuses a stream, and you lose an afternoon blaming the switch.
| Camera | Bitrate each | Eight of them |
|---|---|---|
| 4MP, H.265+ | 4 to 6 Mbps | 32 to 48 Mbps |
| 8MP / 4K, H.265+ | 8 to 12 Mbps | 64 to 96 Mbps |
| 8MP with 24/7 colour | 10 to 14 Mbps | 80 to 112 Mbps |
Eight 4K cameras on an 80 Mbps recorder is tight. Tight enough that we talk people out of it over the counter most weeks. On a 160 Mbps unit you can stop thinking about it and get on with the install. The number is right there on the datasheet, listed as incoming or inbound bandwidth. Ten seconds to check.
PoE ports
A sixteen-channel NVR very often has eight PoE ports. Not sixteen. The other eight channels are expected to arrive from a switch somewhere else on the network, which is a perfectly normal way to build a system and a genuinely annoying thing to discover on site with eight cameras already up the wall and the van half unloaded.
So count the ports separately from the channels. Then look at the total PoE budget in watts rather than the per-port rating, because a switch can offer 30W on every port and still only have 65W to hand out across all of them. People find that out the hard way, one camera at a time, as the last few on the row start rebooting themselves.
Storage
The arithmetic is not complicated.
Total Mbps ÷ 8 × 3600 × 24 × days ÷ 1,000,000 = terabytes
Eight 4K cameras at 10 Mbps each is 80 Mbps, which works out at roughly 0.9 TB a day, so a month of continuous recording wants somewhere around 27 TB. Motion-triggered recording brings that down a long way. How far depends entirely on how busy the site is, and a car park on a main road is not a locked compound behind a gate. Size from the continuous figure anyway. Nobody has ever complained about having too much recording.
Use surveillance-rated drives. A desktop drive will run for a while and then die, because it was never designed to take sustained writes from eight streams at once, and it tends to go at exactly the point you need the footage. We’d rather lose the sale than put a green desktop drive into a recorder that runs all night.
Buy bigger than you need
A client who wanted four cameras in March wants six by Christmas. That happens often enough that we build it into the quote now. Four channels to eight costs very little on the day. Swapping a full four-channel recorder out eighteen months later costs you the unit, plus the labour on top. It also costs you the conversation about why the kit you sold them needs replacing already.
Saving a few quid at the specifying stage is a false economy and most installers have learned it once, expensively. Ring us on 0121 655 0146 for a second opinion on a spec before you order, or have a look through the recorders we carry. Most lines are not held in any depth, so if it isn’t on the shelf and the order lands before noon, we can usually have it here next day. A few lines are trade only and need an approved account.
Frequently asked questions
What size NVR do I need for 8 cameras?
Eight channels at the minimum, but check the incoming bandwidth before anything else. For eight 4K cameras, look for 128 Mbps or more and eight PoE ports. A sixteen-channel unit costs a little more now and saves you a replacement later.
Can I connect more cameras than the NVR has channels?
No. It is a hard limit. Add a second recorder or move up a size.
Do I need a PoE switch as well as the NVR?
Only if you have more cameras than the recorder has PoE ports, or a camera sits further than 100 metres from the recorder. That is where Ethernet gives up.
How much hard drive space do I need for 30 days?
About 27 TB for eight 4K cameras recording continuously. Motion-only recording typically halves it, sometimes better than that on a quiet site.