Why Storage Estimation Matters
Running out of storage means your system begins overwriting older footage before incidents are discovered and reported. Most theft, fraud, and liability claims aren't discovered immediately — a common scenario is reviewing footage 10–14 days after an incident when a missing item is noticed or an injury claim is filed. If your system only retains 3–5 days, that footage is gone.
Oversizing storage adds unnecessary upfront cost. Getting it right requires understanding the variables that drive storage consumption.
The Formula
Storage required (in GB) = Bitrate (Mbps) ÷ 8 × 3600 × 24 × Retention Days × Camera Count ÷ 1000
Simplified: Storage (GB) = Bitrate (Mbps) × 10.8 × Retention Days × Cameras
Where 10.8 = (3600 seconds/hour × 24 hours) ÷ (8 bits/byte × 1000 MB/GB)
4 cameras at 4MP H.265 (avg bitrate ~2 Mbps/camera), 30 days retention:
2 × 10.8 × 30 × 4 = 2,592 GB ≈ 2.6 TB. Add 20% buffer → 4 TB drive minimum.
Key Variables
Bitrate
Bitrate is the primary variable. Actual bitrates depend on resolution, frame rate, scene activity (more movement = more bitrate in variable bitrate encoding), and compression codec.
| Resolution | Codec | Typical Bitrate |
|---|---|---|
| 1080p / 2MP | H.264 | 2–4 Mbps |
| 1080p / 2MP | H.265 | 1–2 Mbps |
| 4MP | H.264 | 4–8 Mbps |
| 4MP | H.265 | 2–4 Mbps |
| 4K / 8MP | H.264 | 8–16 Mbps |
| 4K / 8MP | H.265 | 4–8 Mbps |
Frame Rate
Security cameras are typically configured at 15fps or 30fps. 15fps reduces storage by approximately 50% vs. 30fps with minimal impact on usability for most security applications — 15fps produces smooth-enough footage for identification and event reconstruction. Use 30fps for high-speed capture applications (register areas, fast-moving scenarios).
H.265 vs. H.264
H.265 (HEVC) compression is approximately 50% more efficient than H.264 at the same quality level. If your camera system supports H.265, enabling it halves storage requirements. Most cameras manufactured after 2018 support H.265. This is one of the highest-leverage configuration choices in any camera system.
Continuous vs. Motion-Only Recording
Configuring cameras to record only on motion detection can reduce storage consumption by 60–80% in low-traffic areas. The risk: motion-based recording can miss slow-moving subjects, and the transition period at the beginning of a triggered recording can miss the initiating event. A hybrid approach — continuous recording at reduced frame rate / quality, switching to full quality on motion — provides complete coverage without the storage overhead of full-time high-bitrate recording.
Storage Estimates by System Size
| System | Resolution | Codec | FPS | Retention | Drive Size |
|---|---|---|---|---|---|
| 4 cameras (home) | 4MP | H.265 | 15 | 30 days | 4 TB |
| 8 cameras (small business) | 4MP | H.265 | 15 | 30 days | 8 TB |
| 16 cameras (commercial) | 4MP | H.265 | 15 | 30 days | 16 TB |
| 16 cameras (commercial) | 4K | H.265 | 15 | 30 days | 32 TB |
| 32 cameras (retail/warehouse) | 4MP | H.265 | 15 | 30 days | 32 TB |
Always add 20–30% buffer beyond your calculated requirement. This accounts for scene complexity variations (busy areas use more bitrate than quiet ones), future camera additions, and drive degradation over time. An under-sized drive that fills up and starts overwriting footage during the week you have an incident is a costly mistake.
Retention Requirements by Use Case
- Residential: 14–30 days is standard. 30 days covers nearly all delayed-discovery incidents.
- Retail / small business: 30 days minimum. Shoplifting schemes are often identified when inventory discrepancies surface at end-of-month counts.
- Healthcare: 90 days is common; some facilities require 6 months for compliance and liability management.
- Bank / financial: 90 days minimum; often longer for ATM and transaction-area cameras.
- Insurance requirements: Check your commercial policy — some carriers specify minimum retention periods as a condition of coverage.