Why Storage Sizing Matters
The single most common reason security camera footage is unavailable when needed is overwritten storage. Systems sized without proper calculation run out of space — often in less than 7 days — and begin overwriting older footage before incidents are discovered. Proper storage sizing ensures you retain footage for the required duration regardless of how many cameras are recording.
The Storage Formula
Storage required = Bitrate (Mbps) × Number of cameras × Hours per day × Retention days × Conversion factor
Simplified: Storage (TB) = Bitrate (Mbps) × Cameras × Hours × Days ÷ 8,589,934
The conversion factor (8,589,934) converts megabits to terabytes.
Typical Bitrates by Resolution and Compression
| Resolution | H.264 (Mbps) | H.265 (Mbps) | H.265+ (Mbps) |
|---|---|---|---|
| 2MP (1080p) | 4–6 | 2–3 | 1–1.5 |
| 4MP | 8–12 | 4–6 | 2–3 |
| 8MP (4K) | 16–24 | 8–12 | 4–6 |
| PTZ (4K) | 20–32 | 10–16 | 5–8 |
H.265+ ("Smart Coding") dramatically reduces storage requirements with minimal quality impact — always enable it if supported by your cameras and NVR.
Worked Example: 16-Camera Office Building
Scenario: 16 cameras at 4MP resolution using H.265+, recording 24/7, 30-day retention target
- Bitrate per camera: 2.5 Mbps (H.265+ at 4MP)
- Total bitrate: 16 × 2.5 = 40 Mbps
- Daily data: 40 Mbps × 86,400 seconds ÷ 8 = 432,000 MB = 432 GB/day
- 30-day total: 432 GB × 30 = 12,960 GB ≈ 13 TB
Result: An NVR with two 8TB drives (16TB usable in RAID-1) provides 30-day retention with headroom.
Motion-Only Recording: The Storage Multiplier
If cameras record only during motion events (not continuously), storage requirements drop dramatically. A typical commercial environment with moderate activity may trigger motion 20–40% of the time. The same 16-camera system with motion-only recording at 30% activity rate would require only 3.9 TB for 30 days — a 70% reduction.
However, motion-only recording creates gaps. If a camera is triggered by a criminal who deliberately avoids motion zones, or if the PIR/analytics misses a slow-moving intruder, that activity is never recorded. For security-critical applications, continuous recording with motion-triggered alerts is recommended.
Bandwidth Considerations for Remote Access
Remote live viewing requires upstream bandwidth from your site's internet connection. At 4MP H.265+, a single live stream requires approximately 2–4 Mbps upload. Viewing 8 cameras simultaneously requires 16–32 Mbps upload — this exceeds the upstream capacity of many business-grade internet connections.
Solutions: Substream recording (separate low-resolution stream for remote viewing), NVR-side transcoding to reduce stream quality for mobile clients, or upgrading to a business fiber connection with symmetrical speeds.
Quick Reference: Storage by Camera Count (4MP H.265+, 30 days, 24/7)
- 4 cameras → ~3.2 TB
- 8 cameras → ~6.5 TB
- 16 cameras → ~13 TB
- 32 cameras → ~26 TB
- 64 cameras → ~52 TB
Hard Drive Selection
Always use surveillance-rated hard drives (Seagate SkyHawk, Western Digital Purple, or equivalent). Desktop drives are rated for 8 hours/day use — they fail prematurely in 24/7 recording environments. Surveillance drives are rated for continuous operation, have error recovery settings tuned for video recording, and include vibration compensation for multi-drive enclosures.
Need Help Sizing Your System?
IDS CCTV provides storage and bandwidth calculations as part of every system design. Contact us with your camera count, resolution preference, and retention requirements and we'll specify the correct NVR and drive configuration for your installation.
