Short answer: on a typical 4-camera Brisbane home CCTV system with 4K (8MP) cameras recording motion-only at 30 fps, you’ll get about 21 days of retention on a 4 TB drive. Drop to 8 fps and you double that to 42 days. Add 4 more cameras and you halve it. Step up to 8 TB and you double again. The trick is matching retention to actual review needs — almost no Brisbane homeowner reviews more than 14 days back, but commercial sites with insurance audit needs require 60-90 days.
The storage maths
Three variables drive CCTV storage usage:
- Resolution + bitrate: 4K (8MP) at H.265 averages ~3.5 Mbps. 4MP averages ~2.0 Mbps. 2MP averages ~1.0 Mbps. Multiply by frames per second.
- Frame rate: 30 fps is real-time smoothness. 8 fps is enough to identify a person walking through. 4 fps is enough for slow-paced incidents. Lower frame rate = much lower storage.
- Motion vs continuous: Motion-only typically captures 5-15% of any given hour (active scene with people moving). Continuous captures 100%.
Practical formula: cameras × bitrate × hours × motion factor = bytes used.
Worked examples
Typical Brisbane home — 4 cameras, 4K, 30 fps motion-only, 4 TB HDD: 4 × 3.5 Mbps × 24 × 0.10 motion factor = ~3.4 GB/day per camera = ~13.5 GB/day total = ~22 days on 4 TB.
Same setup at 8 fps motion-only: ~9 GB/day total = ~42 days on 4 TB.
8-camera commercial — 4K, 30 fps motion-only, 8 TB: 8 × 3.5 × 24 × 0.10 = ~27 GB/day = ~28 days. Bump to 16 TB: ~56 days.
Body corporate 12-camera site — 4K, 8 fps continuous, 16 TB: ~50 GB/day = ~28 days. RAID-1 cuts effective storage in half: ~14 days. For 30-day mandatory retention this site needs 32 TB raw.
What changes the maths
- Smart codecs: Dahua’s H.265+ adapts bitrate to scene complexity, saving 30-50% on quiet scenes. Real-world numbers above already include H.265+.
- AI motion (TiOC): Reduces “motion” events from 200/day to 5-15/day, roughly halving the motion factor. Effective retention on a TiOC system is closer to 40-50 days on 4 TB at 30 fps.
- Audio: Adds ~64 kbps per channel. Negligible for 4K, but doubles 720p bitrate.
Picking the right size
Mr Secured’s recommended Brisbane drives: 4 TB for 4-camera residential, 8 TB for 6-8 camera residential or 4-camera commercial, 16-32 TB for any commercial site with audit-required retention. Always WD Purple or Seagate SkyHawk — drives spec’d for 24/7 surveillance write loads.
Get a CCTV retention quote sized for your site: mrsecured.com.au/contact or call 0490 130 339.
