Demystifying CCTV Storage & Bandwidth Math: How We Sized Hard Disk Retention for Nepal

Whether you are designing a surveillance system for a university campus, commercial bank vault, or office building in Nepal, calculating accurate **hard disk drive (HDD) capacity** and **network bandwidth** is a fundamental engineering requirement. As a **Geomatics Engineering student at Kathmandu University**, data math and spatial calculations are second nature to me. When working with **E Three Sales & Services Pvt. Ltd.** to build their online **CCTV Storage Calculator**, we focused on making complex bitrate formulas intuitive for Nepalese installers. ### 1. The Fundamental CCTV Storage Calculation Formula To calculate how many Gigabytes (GB) a single camera records in 24 hours, use this bitrate formula: $$\text{Daily Storage (GB)} = \frac{\text{Bitrate (Mbps)} \times 3600 \text{ seconds/hour} \times \text{Recording Hours/Day}}{8000 \text{ Megabits/GB}}$$ For example, a **4MP IP camera** encoding in **Smart H.265+** at 15 FPS consumes roughly **2.2 Mbps**. Running 24 hours continuous, that camera generates **23.76 GB per day**. ### 2. Bitrate Scaling across Resolutions & Compression Codecs - **2MP / 1080p (Full HD)**: ~1.2 Mbps on Smart H.265+ (12.96 GB/day) - **4MP / 2K (QHD)**: ~2.2 Mbps on Smart H.265+ (23.76 GB/day) - **8MP / 4K (Ultra HD)**: ~4.5 Mbps on Smart H.265+ (48.60 GB/day) Switching from legacy **H.264** (which consumes 8.0 Mbps for 4MP) to **Smart H.265+** reduces total hard drive storage requirements by up to 70%! ### 3. Matching Mandatory Bank Retention Periods (30 to 90 Days) in Nepal Nepalese financial institutions and government security mandates often require **30, 45, or 60 days of un-overwritten video retention**. For a 16-camera 4MP system running 30 days retention: $$\text{Total Storage Needed} = 16 \text{ cams} \times 23.76 \text{ GB/day} \times 30 \text{ days} = 11,404.8 \text{ GB } (\approx 11.4 \text{ TB})$$ Adding a 15% safety buffer for RAID formatting and motion spikes brings total required capacity to **13.1 TB**, which is perfectly fulfilled by **two 8TB WD Purple Surveillance Hard Drives**. Try our interactive **[CCTV Storage & Bandwidth Calculator](/cctv-storage-calculator)** online to pick specific Dahua camera models, set retention days, and generate official NVR & WD Purple HDD recommendations!