Nothing is worse than needing footage from last week and finding the recorder already overwrote it. Storage is the part of a camera system people size by guesswork, then regret. This guide shows how to estimate the storage your cameras actually produce, how many days of retention you can keep, and how to pick the right drive so nothing important disappears.
What determines how much storage you need
Recorded size depends on four things: resolution, frame rate, compression codec, and how much motion is in the scene. The single biggest lever is the codec. H.265 typically halves the file size of H.264 for the same image. Motion matters too, a busy street records far more data than a still hallway, because video compression stores change.
The rough per-camera bitrate
A practical way to estimate is by bitrate in megabits per second (Mbps). Common ballpark figures with H.265:
| Resolution | Typical bitrate (H.265) |
| 2MP (1080p) | 2-4 Mbps |
| 4MP | 4-6 Mbps |
| 8MP (4K) | 8-12 Mbps |
These vary with scene activity. Check your camera’s own bitrate setting for a real number rather than a guess.
The storage formula
Storage in gigabytes for one camera over a period is roughly: bitrate (Mbps) divided by 8, times 3600, times hours per day, times days, divided by 1000. In plain terms, a 4 Mbps camera recording continuously uses about 43 GB per day, or roughly 1.3 TB per month. Multiply by the number of cameras.
So eight 4MP cameras at 4 Mbps recording 24/7 for 30 days need about 10 TB. If you only need 14 days, that halves to about 5 TB.
Continuous versus motion-only recording
Motion-triggered recording can cut storage dramatically in quiet scenes, sometimes by 60-80 percent, because empty hours are not saved. The tradeoff is the risk of missing an event if detection is poorly tuned or triggers late. For high-value areas, continuous recording is safer. For low-traffic zones, motion recording stretches the same drive much further.
A real scenario
A small warehouse installed six 4MP cameras with a 2 TB drive that came in the bundle. At continuous 24/7 recording that drive held only about five days. After a theft was discovered eight days later, the footage was already gone. Switching four low-traffic cameras to motion recording and adding a 6 TB surveillance drive pushed retention past 30 days without changing the cameras.
Common mistakes and how to fix them
- Trusting the bundled drive. Fix: calculate your real need first; kit drives are often sized to look cheap, not to keep footage.
- Using a desktop hard drive. Fix: use a surveillance-rated drive built for 24/7 writing; desktop drives fail early under constant recording.
- Recording everything at max resolution and frame rate. Fix: drop overview cameras to a lower frame rate; 15 fps is plenty for most surveillance.
- Ignoring the codec. Fix: enable H.265 if the recorder and cameras support it to roughly halve storage.
- No redundancy for critical footage. Fix: for important sites, use a second drive or off-site backup so a single disk failure does not erase everything.
Action checklist
- Note each camera’s resolution and set a realistic bitrate.
- Decide the retention you truly need, often 14-30 days.
- Apply the formula per camera and sum the totals.
- Enable H.265 and set overview cameras to 15 fps.
- Use motion recording for low-traffic zones only.
- Buy a surveillance-rated drive with headroom above your estimate.
- Confirm your NVR supports the drive capacity you plan to install.
Conclusion and next step
Storage is simple math once you know your bitrate and retention target. Estimate honestly, choose the right codec, and buy a proper surveillance drive with room to spare. Your next step: open your recorder settings, read the actual bitrate of each camera, and run the numbers before ordering a disk.
FAQ
How many days can a 2 TB drive hold?
It depends on cameras and settings. As a rough guide, one 4MP camera on H.265 recording 24/7 fills about 1.3 TB per month, so a 2 TB drive holds roughly six weeks for a single camera, but only days across several cameras.
Do I need a special hard drive for CCTV?
Yes, use a surveillance-rated drive designed for constant writing and multiple video streams. Ordinary desktop drives wear out quickly under 24/7 recording.
Does H.265 really save that much?
In practice it usually cuts file size by about half compared with H.264 at similar quality, effectively doubling how many days the same drive holds.
Is motion recording safe to rely on?
It saves space but can miss events if detection is slow or poorly tuned. Use continuous recording for critical areas and motion recording for quiet zones.
References
Storage sizing and drive-endurance guidance here reflects widely published material from surveillance drive makers such as Western Digital (WD Purple) and Seagate (SkyHawk), and standard H.264/H.265 codec behavior.