A CCTV storage calculation starts with one number per camera: its bitrate. From that number come the disk capacity, the channel count of the network video recorder (NVR), and the bandwidth on switches and uplinks. Guesswork usually ends one of two ways: recordings overwritten before the required period, or disks and recorders far larger than needed.
This guide walks through the calculation step by step: how H.265 compares with H.264, how resolution, frame rate and recording mode change the result, what RAID takes away, and how to check PoE switch ports and uplinks. A worked example shows the arithmetic. It sits alongside AZEIDK’s security and surveillance systems work with Hikvision and Dahua cameras.
Key takeaways
- The core rule: storage = total bitrate × recording time. Every 1 Mbps recorded continuously needs about 10.8 GB per day.
- Bitrate depends on resolution, frame rate, codec, scene and lighting. Take it from the actual camera settings or the manufacturer’s calculator, not from a generic figure.
- The ITU states that H.265 needs about half the bitrate of H.264 for similar quality. Real savings vary by scene.
- RAID 5 gives up one disk’s capacity and RAID 6 gives up two. Add a reserve margin on top.
- Disk space is not enough on its own: the NVR must accept the incoming bandwidth, and switch uplinks and PoE budgets must carry the load.
- Retention in Saudi Arabia is set by the Security Conditions and Requirements Document issued under the Law on the Use of Security Surveillance Cameras. Check it before you calculate.
Where to start a CCTV storage calculation
Every calculation needs a camera schedule, which comes out of camera placement and coverage planning (see CCTV camera placement and coverage). For each camera, record:
- Resolution: for example 2, 4 or 8 MP (4K).
- Frame rate (fps): the recorded frame rate, not the camera’s maximum.
- Codec: H.264, H.265, or the manufacturer’s smart codec built on top of them.
- Recording mode: continuous, motion/event, or a schedule combining both.
- Required retention: in days, per the facility’s regulatory requirements and project documents.
Then set a bitrate for each group of similar cameras. The most reliable source is the camera itself, running the approved settings on site, followed by the manufacturer’s disk calculator or the values recommended in the datasheet and user manual.
What drives bitrate
Bitrate is not a fixed property of a camera. The same model can produce very different figures in a steadily lit corridor and in a busy car park at night.
| Factor | Effect on bitrate | Design note |
|---|---|---|
| Resolution | Rises with pixel count | Use high resolution only where identification needs it |
| Frame rate | Rises with fps, though not always linearly | Entrances and cash points need more fps than quiet corridors |
| Codec | H.265 is lower than H.264 for similar quality | Confirm the NVR and viewing software support the codec |
| Scene activity | Movement, trees and rain push it up | Use VBR with a sensible cap |
| Lighting and night mode | Low-light noise raises it on many cameras | Size for the worst case, not daytime |
| I-frame interval (GOP) | A short interval raises it | Use the value recommended in the camera manual |
H.265 versus H.264
When the ITU approved H.265/HEVC in January 2013, it stated that the new codec needs about half the bitrate of H.264 for comparable quality. Treat that as a reference ratio, not a guarantee: real savings depend on the scene and settings. Manufacturers also offer smart codecs on top of H.265, such as H.265+ supported by the Hikvision NVR below, which aim to cut bitrate further in quiet scenes. Base the design on measured or conservative values, not on the best advertised saving.
The core formula and unit conversion
Bitrate is measured in megabits per second (Mbps) and storage in bytes. There are eight bits in a byte and 86,400 seconds in a day, so:
- Daily storage (GB) = bitrate (Mbps) × 86,400 ÷ 8 ÷ 1,000 = bitrate × 10.8.
- Total storage = daily storage × retention days × recording duty (1 for continuous).
- Required disk capacity = total storage × (1 + reserve margin).
Watch the units. Disk makers quote terabytes in decimal (1012 bytes), while many operating systems show binary units, so a “10 TB” disk appears as about 9.1 and formatting takes a little more. That is one more reason to keep a margin.
RAID and usable capacity
Multi-bay NVRs use RAID to protect recordings against a disk failure. Each level has a capacity cost:
- No RAID: all capacity is usable, but a failed disk loses its recordings.
- RAID 1: mirrored, so usable capacity is half the total.
- RAID 5: usable = (disks − 1) × disk size; tolerates one failed disk.
- RAID 6: usable = (disks − 2) × disk size; tolerates two failed disks.
RAID support, levels, bay count and maximum disk size differ between recorders. Take them from the official datasheet of the exact model, and prefer surveillance-grade disks on the manufacturer’s compatibility list.
Worked example (illustrative)
This is a hypothetical example to show the method. It is not AZEIDK project data. The bitrates are assumptions; real values come from the selected cameras and their settings.
A commercial building has 32 cameras: 24 at 4 MP with an assumed 4 Mbps each, and 8 at 8 MP with an assumed 8 Mbps each. All use H.265 and record continuously, with an assumed retention of 30 days.
| Step | Calculation | Result |
|---|---|---|
| 4 MP cameras | 24 × 4 Mbps | 96 Mbps |
| 8 MP cameras | 8 × 8 Mbps | 64 Mbps |
| Total incoming bitrate | 96 + 64 | 160 Mbps |
| Daily storage | 160 × 10.8 | 1,728 GB (about 1.73 TB) |
| 30 days | 1,728 × 30 | 51,840 GB (about 51.84 TB) |
| With 20% reserve | 51.84 × 1.2 | about 62.2 TB |
| 8 × 10 TB in RAID 5 | (8 − 1) × 10 | 70 TB usable: sufficient |
| 8 × 10 TB in RAID 6 | (8 − 2) × 10 | 60 TB usable: short; a ninth disk gives 70 TB |
With H.264, assuming the bitrate doubles, the total becomes 320 Mbps, about 3.46 TB per day and about 103.7 TB for 30 days before margin. The codec choice alone can double the disk count.
If the cameras recorded on motion only and actual recording time averaged about 40% of the day (an assumption), 30 days would drop to about 20.7 TB. Motion share is hard to predict, though, and slow or poorly lit events can be missed. Critical cameras are better recorded continuously, and event-based designs should use a conservative motion estimate.
Bandwidth: NVR, switches and uplinks
NVR incoming bandwidth
Every NVR has an incoming bandwidth limit separate from its channel count. The example above needs at least 32 channels, incoming bandwidth comfortably above 160 Mbps, and enough bays for the chosen RAID level. Outgoing bandwidth depends on how many users view live video or play back recordings remotely at the same time.
An example from AZEIDK’s range: the Hikvision DS-7608NXI-K1(B) NVR page lists 8 IP channels, 80 Mbps incoming bandwidth, H.265, H.265+, H.264 and H.264+, and one SATA bay for a disk up to 10 TB. It suits a small site, not the example project. With 8 cameras at an assumed 4 Mbps, incoming load is 32 Mbps, daily storage about 345.6 GB, and a 10 TB disk lasts about 29 days at nominal capacity, and less in practice once binary units, formatting and margin are counted. The page’s spec table names the PoE variant DS-7608NXI-K1/8P(B), so confirm the exact version on the datasheet before ordering.
Switch ports, uplinks and PoE budget
At each switch, check three things: port speed per camera, the uplink that carries all cameras towards the NVR or core switch, and the total PoE budget. The Hikvision DS-3E1309P-EI switch page and Hikvision’s official datasheet list 8 PoE ports at 10/100 Mbps, one gigabit uplink, and a 110 W total PoE budget with up to 30 W per port under IEEE 802.3af/at.
- Eight cameras at 8 Mbps put 64 Mbps on the uplink, well within a 1 Gbps link. Add sub-stream and live-view traffic.
- If a camera’s datasheet maximum is 12 W (an assumption, including IR at night), eight cameras need 96 W, inside the 110 W budget. PTZ cameras with heaters need separate checking.
- In larger networks, traffic from several switches converges on the core switch and the NVR port. Size each link for everything that passes through it.
Recording retention in Saudi Arabia
The Law on the Use of Security Surveillance Cameras was issued by Royal Decree No. M/34 dated 7/3/1444 AH. Minister of Interior Decision No. 22688 dated 3/11/1444 AH approved its Implementing Regulation and the Security Conditions and Requirements Document, and was published in Umm Al-Qura. Article 6 of the Implementing Regulation, as published there, provides that when a security incident is reported, the person responsible for the site, activity or facility is notified and signs a written undertaking to keep the recordings until investigation procedures end or for the period set in the Conditions Document, whichever is longer. Article 10 adds that, except for authorised bodies, recordings may not be kept contrary to the period set in the Conditions Document.
In practice, retention days are not assumed. They come from the current Conditions Document and the requirements of the authority overseeing that type of facility, plus a margin for footage held because of a report or investigation. For background on the law, see Surveillance Systems in Saudi Arabia: Market Growth and the Law.
Common mistakes
- Sizing on daytime bitrate: many cameras rise at night or in rain and dust, so storage runs out early.
- Forgetting RAID and margin: treating raw disk capacity as usable.
- Checking channels only: a 32-channel NVR may not accept 32 cameras at 8 MP if the total exceeds its incoming bandwidth.
- Ignoring uplinks: enough switch ports, but an uplink or NVR port that cannot carry the total.
- Exceeding the PoE budget: adding typical rather than maximum datasheet consumption.
- Assuming retention without a reference: using a figure in circulation instead of the official Conditions Document.
- No monitoring after handover: actual retention and disk health are not checked periodically, which belongs in CCTV and security system maintenance.
Frequently asked questions
How many gigabytes does one camera use per day?
Multiply its bitrate in Mbps by 10.8 to get GB per day of continuous recording. A 4 Mbps camera uses about 43.2 GB a day.
Does switching to H.265 halve the disks?
Half is the ITU’s reference ratio for similar quality, but real savings vary with scene and settings. Measure bitrate after commissioning before fixing the final disk count.
Is RAID needed on every project?
Not always, and small single-bay NVRs do not support it. Where losing footage is an operational or regulatory risk, choose an NVR that supports RAID 5 or RAID 6.
How long must CCTV footage be kept in Saudi Arabia?
The Implementing Regulation refers to the period set in the Security Conditions and Requirements Document. If a security incident is reported, footage must be kept until the investigation ends or for that period, whichever is longer. Check the current document for your facility type.
Does live viewing affect storage?
Live viewing adds no storage unless recorded, but it uses the NVR’s outgoing bandwidth and network links, so include it when choosing the NVR and network.
Conclusion
CCTV storage sizing follows a clear chain: a camera schedule, a realistic bitrate per group, daily storage times the approved retention, then RAID and margin. After that, check the NVR’s channels and incoming bandwidth, and the switches’ ports, uplinks and PoE budget.
Preparing a camera schedule for your project? Send us the camera count, resolutions and required retention, and we will propose Hikvision and Dahua recorders, disks and switches with datasheets. Talk to the AZEIDK team
