How CCTV storage is calculated
An IP camera sends a continuous video stream to the network video recorder (NVR). Its size is measured as a bitrate in megabits per second (Mbps). Multiply the bitrate by the recording time and the number of cameras and you get the storage needed per day; multiply again by the number of days you must keep footage and you know how many terabytes to buy.
Storage (GB/day) = bitrate (Mbps) × 3,600 × hours ÷ 8 ÷ 1,000 × share of time recorded
What affects bitrate
- Resolution – more megapixels mean more data. A 4K (8 MP) stream is roughly two to three times a 1080p stream.
- Codec – H.265 compresses about 40 – 50 % better than H.264; "smart" codecs (H.265+, Zipstream, Smart Codec) save more on static scenes.
- Frame rate – 10 – 15 fps is enough for most offices and shops; 25 – 30 fps for cash registers, entrances and license plates.
- Scene complexity – movement, trees, rain, night-time noise and busy streets increase bitrate significantly.
Typical bitrates (15 fps)
| Resolution | H.264 | H.265 | GB per day (H.265, 24/7) |
|---|
| 2 MP 1080p | 4 Mbps | 2.2 Mbps | ≈ 24 GB |
| 4 MP | 6 Mbps | 3.3 Mbps | ≈ 36 GB |
| 8 MP 4K | 12 Mbps | 6.6 Mbps | ≈ 71 GB |
Retention periods
How long you keep footage depends on your industry, insurance and local privacy law. Retail and offices commonly keep 30 days; banks, casinos and cannabis businesses may be required to keep 60 – 90 days or more. Under GDPR and similar laws you should not keep footage longer than necessary, so document your retention period and post signage.
Choosing NVR hard drives
Use drives designed for surveillance: they are tuned for continuous writing from many streams and rated for 24/7 workloads. Leave about 10 % free space. For important systems use RAID 5 or RAID 6 so a single drive failure doesn't erase weeks of evidence – but remember that RAID uses some capacity for protection, which the calculator includes.
Network and power
- Each camera's stream adds to the switch and NVR load; gigabit uplinks are recommended above about 30 – 50 Mbps total.
- Most fixed IP cameras use 4 – 8 W of Power over Ethernet; IR illuminators at night and heaters increase this. PTZ cameras need PoE+ or PoE++.
- Put cameras on a separate VLAN and never expose the NVR directly to the internet – use the vendor's secure cloud relay or a VPN.
- Protect the NVR and PoE switch with a UPS so recording continues during short power cuts.
Frequently asked questions
How much storage does a 4K security camera need?
A 4K camera recording continuously with H.265 at 15 fps uses about 70 GB per day – roughly 2.1 TB for 30 days.
How many days of CCTV footage will 1 TB hold?
With one 1080p H.265 camera recording 24/7, about 40 days. With eight cameras, about five days.
Does motion recording save storage?
Yes. Recording only on motion typically cuts storage by 50 – 85 %, depending on how busy the scene is.
H.264 or H.265 for CCTV?
H.265 needs about half the storage and bandwidth of H.264 for similar quality. Use it if your cameras, NVR and viewing software support it.
Can I use normal hard drives in an NVR?
It's not recommended. Surveillance drives are designed for constant writing from multiple streams and last much longer in NVRs.
About CamVault
CamVault is an independent, free calculator for planning IP security camera systems, NVR storage and network capacity in offices, shops and small businesses. Bitrates are typical averages; your cameras' scene complexity affects results. We are not affiliated with any camera or NVR brand.
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The methodology combines widely published engineering rules of thumb, manufacturer data sheets and the electrical code practices that installers use every day. We review the assumptions regularly and update the calculator when typical product specifications change.
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Last updated: October 28, 2026
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