Short answer: Per camera, gigabytes per day ≈ bitrate in Mbps × 10.8 when recording around the clock. A camera streaming 4 Mbps needs about 43 GB a day, or 1.3 TB for 30 days. Multiply by your cameras, then add 10–20% headroom. Or use the CCTV storage calculator.
Where does the formula come from?
A day has 86,400 seconds. A stream of 1 megabit per second therefore produces 86,400 megabits a day, which is 10,800 megabytes, or 10.8 GB. Everything else is multiplication:
Storage = bitrate (Mbps) × 10.8 × days kept × number of cameras × share of the day recorded
What bitrate does a security camera use?
It depends on resolution, frame rate, codec and how busy the scene is. Your camera’s settings page shows the real number. As rough starting points at 15–25 frames per second:
| Camera | H.264 | H.265 |
|---|---|---|
| 2 MP (1080p) | about 4 Mbps | about 2 Mbps |
| 4 MP | about 6 Mbps | about 3 Mbps |
| 8 MP (4K) | about 12 Mbps | about 6 Mbps |
Night scenes with noise, rain, trees and busy streets push bitrate up; a quiet corridor brings it down. The H.264 vs H.265 post explains why the right-hand column is half the left.
A worked example
Sixteen 4 MP cameras on H.265 at 3 Mbps, recording 24 hours a day, kept for 30 days:
- Per camera per day: 3 × 10.8 = 32.4 GB
- Per camera for 30 days: 32.4 × 30 = 972 GB
- All sixteen: 972 × 16 = 15.6 TB
- With 15% headroom: about 18 TB
Why does my 4 TB disk show less than 4 TB?
Disk makers count a terabyte as 1,000,000,000,000 bytes; operating systems usually count in powers of two. A 4 TB disk shows as about 3.6 “TB” (strictly, TiB). Plan in the smaller number.
How can I need less storage?
- Use H.265 where your cameras and software support it. Often 30–50% smaller for the same picture.
- Turn on the camera’s smart codec, such as Axis Zipstream or Hanwha WiseStream, which lowers bitrate when nothing is moving.
- Record on motion or events for cameras that watch empty spaces. Keep continuous recording for entrances and tills.
- Lower the frame rate. 12–15 fps is plenty for most security footage; 25–30 fps mostly costs disk.
- Keep footage only as long as you need it. Many sites keep 30 days. Data protection rules generally say not to keep personal data longer than necessary, so check what applies to you.
What kind of disks should I use?
Drives built for surveillance or NAS use are designed to write around the clock. RAID protects against a single failed disk, but costs capacity: RAID 5 gives up one disk’s worth, RAID 6 two. RAID is not a backup.
How Supervision helps
Supervision records to your own server’s disks and shows storage used per camera, so you can see which cameras eat the space. The playback calendar is shaded by how much was recorded each day, which makes gaps easy to spot. See how to know when a camera stops recording.
Common questions
How many days of CCTV footage should I keep?
Thirty days is a common default, long enough to notice most incidents. Some industries and countries set their own rules, so check before choosing.
Does recording on motion really save space?
For quiet scenes, a lot: a car park at night may record a few minutes an hour instead of sixty. For busy scenes, little. Pre- and post-event recording adds some back.
Should I record the main stream or the substream?
Record the main stream; that’s the evidence. Use the substream for viewing grids.
Supervision is self-hosted video management software for any camera brand. If this is the kind of problem you're solving, tell us about your cameras and we'll talk it through, or email hello@bipolarfactory.com.