How Much Storage Does a 4-Camera 1080p System Need? A Worked Example
"How big a hard drive do I need for my security cameras?" has a real answer, not just "get a big one." Here's a 4-camera 1080p setup worked all the way through — varied by resolution, camera count, recording hours, and codec — using the same math behind the Security Camera Storage Calculator.
The math in three steps
- Bitrate per camera. A typical 1080p H.264 stream, continuous recording, runs about 4 Mbps.
- Convert to storage per camera per day: 4 Mbps × 0.125 (megabits→megabytes) × 3,600 seconds/hour × 24 hours ÷ 1,024 (MB→GB) = 42.2 GB per camera, per day.
- Multiply by camera count and retention days.
The worked example: 4 cameras, 24/7, three retention windows
| Retention | Total storage needed | Suggested drive |
|---|---|---|
| 30 days | 4.94 TB | 6 TB |
| 60 days | 9.89 TB | 10 TB |
| 90 days | 14.83 TB | 16 TB |
30 days of true 24/7 recording across 4 cameras needs just under 5 TB — a single 6 TB surveillance-rated drive covers it with a little headroom, which is why 6 TB is such a common NVR default.
What resolution does to the number (4 cameras, 24/7, 30-day retention)
| Resolution | Typical bitrate | Total storage (30 days, 4 cams) | Suggested drive |
|---|---|---|---|
| 720p HD (1 MP) | 2 Mbps | 2.47 TB | 3 TB |
| 1080p Full HD (2 MP) | 4 Mbps | 4.94 TB | 6 TB |
| 3 MP | 6 Mbps | 7.42 TB | 8 TB |
| 4 MP / 1440p (2K) | 8 Mbps | 9.89 TB | 10 TB |
| 5 MP | 10 Mbps | 12.36 TB | 14 TB |
| 4K Ultra HD (8 MP) | 16 Mbps | 19.78 TB | 20 TB |
Resolution is by far the biggest lever on storage cost for a fixed camera count and retention window — jumping from 1080p to 4K roughly quadruples the drive requirement for the identical setup, more than doubling or tripling camera count or retention days typically would.
What camera count does to the number (1080p, 24/7, 30-day retention)
| Cameras | Total storage | Suggested drive |
|---|---|---|
| 1 | 1.24 TB | 2 TB |
| 4 | 4.94 TB | 6 TB |
| 8 | 9.89 TB | 10 TB |
| 16 | 19.78 TB | 20 TB |
Storage scales linearly with camera count, which makes it easy to plan incrementally: doubling cameras roughly doubles the drive requirement, with no surprises.
What recording hours per day does to the number (1080p, 4 cameras, 30-day retention)
| Hours/day recorded | Total storage | Suggested drive |
|---|---|---|
| 8 (business hours only) | 1.65 TB | 2 TB |
| 12 | 2.47 TB | 3 TB |
| 16 | 3.30 TB | 4 TB |
| 24 (true continuous) | 4.94 TB | 6 TB |
If continuous 24/7 recording isn't actually necessary — a business that only cares about after-hours coverage, say — recording only outside business hours (roughly the inverse of the 8-hour row above) can cut storage nearly in half versus full continuous recording, without losing any coverage of the hours that actually matter.
H.264 vs. H.265/HEVC: the codec question
Every number above assumes H.264, the more common and broadly compatible codec. H.265/HEVC compresses more efficiently for the same visual quality — roughly half the bitrate for equivalent footage, when both the camera and the NVR support it. Applied to the 4-camera/1080p/30-day baseline: H.264 needs 4.94 TB (a 6 TB drive); the H.265 equivalent, at roughly half the bitrate, needs about 2.47 TB (a 3 TB drive) — effectively doubling how much retention the same physical drive can hold, or halving the drive size needed for the same retention window. The trade-off is compatibility: older cameras, NVRs, and viewing software don't all support H.265, and the encoding itself demands more processing power on both ends.
Common mistakes in storage planning
- Buying storage for the camera count you have today, not the one you'll likely add. Since storage scales linearly per camera, sizing with headroom for 1–2 additional cameras avoids an early drive swap.
- Assuming motion-only recording gives a fixed, predictable saving. It genuinely reduces storage, but the exact savings depend entirely on how much motion a given scene actually has — a quiet backyard camera saves far more than one facing an active sidewalk. Treat published motion-only estimates as optimistic, not guaranteed.
- Ignoring retention requirements that aren't yours to set. Some commercial insurance policies or local regulations specify minimum footage retention — check before assuming a shorter window is acceptable.
- Not accounting for a second stream. Some NVR setups record a full-resolution primary stream plus a lower-resolution "sub-stream" for live viewing — this typically adds a modest overhead beyond the primary-stream numbers above, worth checking against your specific hardware's documentation.
Drive selection: not just size, but rating
The suggested drive sizes above assume a surveillance-rated hard drive, not a general-purpose desktop drive. Surveillance drives are built and firmware-tuned for sustained 24/7 write workloads — continuously writing incoming video — which is a meaningfully different duty cycle than a desktop drive designed for intermittent read/write bursts. Using a standard desktop drive in an always-recording NVR role tends to shorten its working life considerably compared to a drive actually rated for the workload; the price difference between the two is small relative to the cost of a drive failure losing weeks of footage.
RAID and redundancy for larger or higher-stakes setups
A single drive, however well-rated, is a single point of failure — if it fails, all recorded footage on it is gone regardless of how well the storage was sized. Larger installations, or any setup where footage genuinely matters for insurance or liability reasons, are worth pairing with a NVR that supports RAID (multiple drives working together, with redundancy that survives a single drive failure) rather than one large single drive. This roughly doubles the effective storage cost for the same usable capacity in the most common redundant configuration, but converts "a drive failure loses everything" into "a drive failure is a maintenance event," which is a meaningfully different risk profile for a business relying on that footage.
FAQ
Should I round up or down when a calculation lands between two drive sizes?
Round up, and add margin beyond that — a drive that's exactly full at your target retention window leaves no room for a slightly busier month or a camera added later.
Does storage math change for outdoor vs. indoor cameras?
Not from the bitrate/retention math itself, though outdoor cameras exposed to more motion (traffic, weather, wildlife) will produce more data under motion-only recording specifically than a quiet indoor camera would.
What's the single biggest lever if I need to cut my storage requirement?
Resolution, by a wide margin — dropping from 4K to 1080p saves roughly 75% of storage for an identical camera count and retention window, more than any other single change.
Is it worth buying a bigger drive than I currently need?
Usually yes, given how directly storage needs scale with camera count — a modest amount of headroom avoids a drive swap the first time you add a camera or extend retention.
Try your own setup
Plug in your actual camera count, resolution, hours per day, and retention window in the Security Camera Storage Calculator — the table bitrates above are typical H.264 defaults, and the tool lets you override with a manufacturer-specified bitrate if you have one. For deciding how many cameras and what coverage you actually need before sizing storage, see how many cameras a small business actually needs and choosing the right focal length.