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

When designing a commercial security system for a financial institution, hydropower station, university campus, or retail facility in Nepal, calculating accurate hard disk drive (HDD) capacity and network bandwidth is one of the most critical engineering steps.

As an undergraduate student in Geomatics Engineering at Kathmandu University (KU), spatial data modeling, mathematical optimization, and precision analytics are central to my academic work. When I teamed up with E Three Sales & Services Pvt. Ltd. (Teku, Kathmandu)—the official Authorized Distributor of Dahua Technology and Authorized Sole Distributor of Imou in Nepal—I set out to eliminate the guesswork that installers frequently face when sizing CCTV storage setups.

Here is the exact mathematical framework we developed to size hard disk retention for real-world projects across Nepal.

In my conversations with system integrators across Teku and Kathmandu, I frequently encounter two costly mistakes:

• Underestimating HDD Storage: If an NVR overwrites old footage after only 12 days instead of the mandatory 30 days required by Nepal Rastra Bank for financial institutions, the organization risks regulatory fines and lost evidence during police investigations.
• Overestimating HDD Storage: Buying four 10TB enterprise hard drives when two 6TB WD Purple drives would suffice unnecessarily inflates project budgets by tens of thousands of Nepalese Rupees.

Mathematical calculation gives you exact figures based on camera resolution, frame rate, video compression codec, and target retention days.

Instead of memorizing complex textbook equations, here is the clean multiplier rule we use on-site when sizing hard drives in Kathmandu:

• Daily Storage per Camera (GB) = Stream Bitrate (in Mbps) × 10.8

Where does the 10.8 constant multiplier come from? It is simply the 24-hour daily time conversion factor: 3,600 seconds per hour × 24 hours per day = 86,400 seconds. Divide 86,400 seconds by 8,000 Megabits in a Gigabyte, and you get exactly 10.8.

Let's test this multiplier with a real-world example: A popular 4MP (2K) Dahua IP Camera encoding in Smart H.265+ at 15 FPS streams at an average bitrate of 2.2 Mbps.

• Daily Storage per Camera = 2.2 Mbps × 10.8 = 23.76 GB per day

Video compression algorithms have evolved dramatically over the past decade. Switching from legacy H.264 to Dahua’s Smart H.265+ reduces total hard drive storage requirements by up to 73%!

• 2MP / 1080p Full HD @ 15 FPS:
• - Legacy H.264 Codec: 4.0 Mbps (~43.2 GB/day)
• - Standard H.265 Codec: 2.0 Mbps (~21.6 GB/day)
• - Dahua Smart H.265+ Codec: 1.2 Mbps (~12.96 GB/day)

• 4MP / 2K QHD @ 15 FPS:
• - Legacy H.264 Codec: 8.0 Mbps (~86.4 GB/day)
• - Standard H.265 Codec: 4.0 Mbps (~43.2 GB/day)
• - Dahua Smart H.265+ Codec: 2.2 Mbps (~23.76 GB/day)

• 8MP / 4K Ultra HD @ 15 FPS:
• - Legacy H.264 Codec: 16.0 Mbps (~172.8 GB/day)
• - Standard H.265 Codec: 8.0 Mbps (~86.4 GB/day)
• - Dahua Smart H.265+ Codec: 4.5 Mbps (~48.60 GB/day)

Let's walk through a practical sizing scenario for a commercial bank branch in Kathmandu requiring 30 days of continuous 24/7 video retention under Nepal Rastra Bank guidelines:

• System Configuration:
• - 16 × 4MP Dahua WizColor AI IP Cameras (DH-IPC-HFW2449T-S-IL)
• - Recording Profile: 4MP @ 15 FPS, Smart H.265+ Codec (~2.2 Mbps per camera)
• - Target Retention: 30 Full Days (720 Hours)

• Step-by-Step Calculation:
• 1. Daily storage per camera: 2.2 Mbps × 10.8 = 23.76 GB/day
• 2. Daily storage for all 16 cameras: 16 cameras × 23.76 GB = 380.16 GB/day
• 3. Total storage for 30 full days: 380.16 GB/day × 30 days = 11,404.8 GB (approx. 11.41 TB)
• 4. Adding the 15% Safety Buffer: 11.41 TB × 1.15 = 13.12 TB required capacity

A common mistake made by non-specialized installers in Nepal is buying desktop PC hard drives (like WD Blue or Seagate Barracuda) because they cost slightly less upfront.

• Desktop Hard Drives (8x5 Duty Cycle): Designed to run 8 hours a day, 5 days a week, with a workload ratio of 80% Read / 20% Write.
• Surveillance Hard Drives (24x7 Duty Cycle): Dedicated WD Purple (AllFrame AI) and Seagate SkyHawk AI drives are engineered to operate 24 hours a day, 365 days a year, with a heavy 90% Write / 10% Read workload ratio.

Installing desktop drives in an NVR frequently leads to drive overheating, dropped video frames during playback, and complete disc failure within 6 to 12 months.

In addition to hard drive storage, your NVR must have sufficient incoming network bandwidth to handle all camera streams simultaneously without packet loss or stuttering.

For our 16-camera setup operating at 2.2 Mbps per stream:

• Total Incoming Bitrate = 16 cameras × 2.2 Mbps = 35.2 Mbps

Since the Dahua NVR4216-4KS2/I supports up to 160 Mbps incoming bandwidth, a 35.2 Mbps load consumes less than 23% of the NVR’s network capacity—leaving plenty of headroom for smooth PTZ control and multi-channel remote DMSS mobile viewing.

To make these calculations instant for installers, site supervisors, and IT engineers, we built the official interactive [CCTV Storage & Bandwidth Calculator](/cctv-storage-calculator) on the E3 Nepal website.

Simply select your camera resolutions, set your camera count, choose your recording codec, and specify retention days to instantly receive exact hard drive capacity requirements and official WD Purple HDD drive recommendations!