Calculate NVR/DVR hard disk size in TB from camera count, resolution, frame rate, H.264/H.265 compression and retention days — with per-camera GB/day, network bandwidth and surveillance HDD suggestions.
How to Calculate CCTV Storage
CCTV storage sizing answers one question: how many terabytes does the NVR/DVR need to keep the required days of footage from all cameras? Get it wrong in one direction and the system silently overwrites evidence before the retention period ends — a compliance failure in most jurisdictions. Get it wrong the other way and you've paid for drives that never fill. The calculation depends on four things: camera bitrate (driven by resolution, frame rate and codec), recording schedule, number of cameras, and retention days.
CCTV Storage Formula
Storage (GB) = Bitrate (Kbps) × 3600 × Hours/day × Activity% × Days × Cameras ÷ 8 ÷ 1,000,000
Storage (TB) = GB ÷ 1,000 → add 10–20% overhead
The bitrate is the key variable. Typical good-quality bitrates at 25 fps with H.264: 2 MP ≈ 4 Mbps, 4 MP ≈ 6 Mbps, 8 MP (4K) ≈ 14 Mbps. Lower frame rates scale the bitrate down proportionally, and modern codecs cut it dramatically: H.265 needs ~45% less storage than H.264, and smart codecs (H.265+, H.264+, Zipstream) save another 30–50% in low-motion scenes.
Worked Example: 16-Camera Office System
16 × 2 MP cameras, H.265, 15 fps, continuous 24/7 recording, 30-day retention, 10% overhead:
- Bitrate per camera = 4,096 × (15/25) × 0.55 ≈ 1,352 Kbps (≈1.35 Mbps)
- Per camera per day = 1,352 × 86,400 ÷ 8 ÷ 10⁶ ≈ 14.6 GB/day
- Total = 14.6 × 16 × 30 ≈ 7,010 GB = 7.0 TB → with 10% overhead ≈ 7.7 TB → use 1 × 8 TB or 2 × 4 TB surveillance drives
- Network bandwidth ≈ 1.35 × 16 ≈ 22 Mbps — comfortably within a gigabit NVR switch
Design Tips for CCTV Storage
- Use surveillance-rated HDDs. NVRs write 24/7 — desktop drives aren't rated for that duty and fail early. Specify Seagate SkyHawk, WD Purple or equivalent.
- Check local retention rules. Many authorities mandate minimum retention (30, 90, even 180 days for some facilities) — verify before sizing, because retention days scale storage linearly.
- Motion recording saves 50–70% in low-traffic areas, but use continuous recording for critical zones (entrances, cash points) — motion detection can miss slow or partial events.
- Don't forget RAID overhead. RAID 5 loses one drive's capacity, RAID 6 loses two — size the array so usable capacity meets the requirement.
- Verify codec support end-to-end. H.265+ only saves storage if both the camera and the NVR support it; mixed systems fall back to H.264.
- Plan bandwidth too. Storage and network go together — the total Mbps figure from this tool sizes the NVR switch and uplinks.
Frequently Asked Questions
How much storage does 1 CCTV camera use per day?
A 2MP (1080p) camera at 15 fps: ~26 GB/day with H.264 or ~15 GB/day with H.265 (continuous). A 4K camera: ~93 GB/day H.264, ~51 GB/day H.265.
How many days can 1TB record?
About 70 days from one 2MP H.265 camera at 15 fps continuous — or ~38 days with H.264. With four 2MP H.265 cameras, 1 TB lasts roughly 17 days.
How do I calculate CCTV storage in TB?
Storage (GB) = Bitrate (Kbps) × 3600 × hours × days × cameras ÷ 8 ÷ 1,000,000 — then divide by 1,000 for TB and add 10–20% overhead. Or just use the calculator above.
Is H.265 better than H.264 for storage?
Yes — roughly 40–50% less storage at the same quality, and H.265+/smart codecs save even more in static scenes. Confirm both camera and NVR support it.
Which hard disk should I use for CCTV?
Surveillance-rated drives (Seagate SkyHawk, WD Purple) built for 24/7 write workloads. Standard desktop drives fail prematurely in NVR duty.
Disclaimer: Bitrates vary with scene complexity, quality settings and manufacturer implementation. Use the custom bitrate field with datasheet values for final design, and verify retention compliance with local regulations.