How much storage does a CCTV system need?
Eight 4MP cameras recording continuously on H.265, kept for a month, need about 11 TB. That is one 12 TB drive. Change any of it below and the number moves with you.
One camera type at a time. For a mixed system, run it once for each group of cameras and add the answers together.
The arithmetic, in the open
Nothing here is proprietary. A camera writes at a steady bitrate, and storage is that bitrate multiplied by time. Everything else is a judgement about how much time.
GB per hour = Mbps × 0.45
GB total = GB per hour
× hours a day
× days kept
× cameras
× motion factor
+ spare capacity
Storage is quoted the way drives are labelled: 1 GB is 1,000 MB and 1 TB is 1,000 GB. A lot of calculators divide by 1,024 and still print GB, which puts the answer about ten percent away from the number on the box you are about to buy.
Worked through
Eight 4MP cameras on H.265, recording continuously, kept for 30 days, with ten percent spare capacity.
- 4 Mbps is the typical bitratefor 4MP on H.265
- 4 × 0.45 = 1.8 GBrecorded every hour
- × 24 hours = 43.2 GBper camera, per day
- × 8 cameras = 345.6 GBacross the system, per day
- × 30 days = 10,368 GBfor the month
- + 10% = 11,405 GBwith spare capacity
- = 11.4 TBso a 12 TB drive
Typical bitrates
In Mbps, at 15 to 20 frames a second and normal scene complexity. Starting points rather than physics: a busy street records larger than an empty corridor, and smart coding on a modern camera can pull these down considerably. If you know what your cameras are set to, that number beats this table.
| Resolution | H.264 | H.265 | One camera, 24 hours |
|---|---|---|---|
| 2MP1080p | 4 Mbps | 2 Mbps | 21.6 GB on H.265 |
| 4MP2K | 8 Mbps | 4 Mbps | 43.2 GB on H.265 |
| 5MP | 10 Mbps | 5 Mbps | 54.0 GB on H.265 |
| 8MP4K | 16 Mbps | 8 Mbps | 86.4 GB on H.265 |
| 12MP | 24 Mbps | 12 Mbps | 129.6 GB on H.265 |
Questions we get asked
- Does H.265 really halve the storage?
- Close to it, in practice. H.265 encodes the same picture in roughly half the bitrate of H.264, so a camera that needs 8 Mbps on H.264 needs about 4 Mbps on H.265. The saving is largest on scenes that do not change much. Both the camera and the recorder have to support it, and a very old recorder may not, which is worth checking before you plan a system around the smaller number.
- Does recording on motion save space?
- It can save a great deal, and it can save almost nothing. A store room that sees three people a day might record a tenth of the time. A shop floor or a road frontage triggers so often that continuous recording uses barely more. The calculator lets you pick how busy the site is, but this is the roughest figure on the page. If the footage matters, size the drive for continuous recording and treat motion as headroom.
- What happens when the drive is full?
- The recorder overwrites the oldest footage, so you never lose the current recording, you lose the far end of the history. That is why retention is the number that matters: a drive sized for 30 days holds roughly 30 days, then starts writing over day one. If you need to be able to look back further than that, the drive is the thing to change.
- Why is the answer different from the drive size I bought?
- A drive labelled 12 TB formats to a little less, because the manufacturer counts in thousands and the computer counts in 1024s. This calculator quotes storage the way drives are labelled, and the spare capacity margin absorbs the difference along with the space you want left over.
We will size it against the actual site.
A calculator works from the numbers you give it. A survey works from the entrances, the boundary and the light. The survey is free.