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Graduvex

CCTV storage calculator: how many terabytes do you need?

Sizing a NAS or CCTV recorder comes down to one multiplication nobody writes out: camera bitrate × recording time × retention. This tool writes it out — and also tells you what your cameras will do to your network.

Count only the ones that record (not doorbells that stream on demand).

In the camera’s interface, the main stream “bitrate” setting. Ballpark: 2–4 for 1080p H.265, 6–8 for 4K.

24 for continuous recording; 4 to 8 in practice for motion-triggered recording.

How long footage is kept before being overwritten. 30 days is a common choice.

Storage required

5.18TB

Plan for a multi-bay NAS, with surveillance-rated drives.

Combined network throughput
16Mbit/s

Comfortable on an ordinary gigabit network.

The method

A camera encoding at 4 Mbit/s produces 4 megabits every second, which you divide by 8 to get bytes. Over a full day that is roughly 43 GB; multiply by the number of cameras and the days you keep.

The maths is done in base 10 (1 TB = 1,000 GB), like drive manufacturers: the result compares directly with the label on the drive you will buy.

The combined network throughput is the sum of all streams: it decides whether a plain gigabit switch is enough between cameras and recorder.

In the formula: n is the number of cameras, b the per-camera bitrate (Mbit/s), h the hours per day, j the retention days.

storage (TB) = n × b × 3,600 × h × j / 8 / 1,000,000 · total throughput = n × b

Good to know

  • Actual bitrate varies with the scene: a busy street at night (noise, rain) produces more data than an empty hallway. Treat the configured bitrate as a ceiling, not a guaranteed average.
  • H.265 roughly halves H.264’s bitrate at equal quality: the codec you pick weighs more than resolution in the storage bill.
  • Motion-triggered recording cuts volume a lot, but size as if detected hours were full: one windy month triggers around the clock.
  • A surveillance-rated drive (built for continuous writes) does not share firmware with a desktop drive: at equal capacity, it is the one to buy.
  • Keep 10–15% free space: a full volume slows writes and some NVRs stop instead of overwriting.

FAQ

What bitrate should I set on my cameras?

With H.265: 2–4 Mbit/s is enough at 1080p, 6–8 Mbit/s at 4K, for identification-grade footage. Double those for H.264. Going higher improves the image marginally and doubles the storage bill.

Why does my 4 TB drive show only 3.6 TB?

Manufacturers count in base 10 (1 TB = 1,000⁴ bytes), many systems display base 2 (1 TiB = 1,024⁴ bytes): 4 TB is 3.64 TiB. This tool works in base 10, so it compares with the drive label, not with what Windows displays.

Continuous or motion-triggered recording?

Continuous guarantees nothing is missing — which is what insurers and police ask for — at the cost of storage. Motion detection divides volume by 3 to 6, but sometimes misses the start of an event and triggers on rain or headlights. The common compromise: continuous at low quality + full quality on detection, if the camera supports it.

Does RAID change the calculation?

Yes, on usable capacity: RAID 1 halves it, RAID 5 costs one drive of the set. This tool’s figure is the NET need: add redundancy on top. And remember RAID protects against a drive failure, not against the recorder being stolen.

How long am I allowed to keep footage?

Rules vary by country: in the EU, data-protection authorities commonly recommend keeping routine footage no longer than about a month unless you can justify more. Filming beyond your own property (streets, neighbours) is restricted almost everywhere. Check the rules that apply to your situation.

Can an SD card in the camera replace the NAS?

For a few days of motion-triggered clips, yes. For continuous recording, do the maths: one camera at 4 Mbit/s fills a 256 GB card in under 6 days, and cards wear out fast under permanent writes. The SD card is a fallback (if the NAS goes down), not the main storage.

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