Choosing a CCTV hard drive doesn’t start with asking for the biggest capacity; it starts with the number of cameras, how long recordings are kept, the actual bitrate and the recording method. In this guide from the Shaikh Alkar team in Jordan, we explain how to calculate the space step by step, with a practical example for four-camera systems and a table showing when to consider 500GB, 1TB, 2TB or 4TB. The figures here are estimates to make comparison easier, not a promise of a fixed recording time.
What determines how long CCTV cameras record?
The required capacity depends on five main factors: the number of cameras recording at the same time, the average bitrate of each camera, the number of days recordings are kept, the codec such as H.264 or H.265, and whether recording is continuous all day or motion-based. Frame rate (FPS), resolution, scene complexity, night lighting and audio (if recorded) also have an effect. Knowing the camera is 2MP or 5MP isn’t enough to determine the number of recording days, because compression and quality settings can change the amount of data a lot.
How to calculate drive space from bitrate
Look in the DVR or NVR settings for each channel’s bitrate in Mbps, preferably the average actual usage after running the system in near-real conditions. A megabit (Mb) differs from a megabyte (MB): every 8 bits equal one byte. To calculate daily capacity in decimal units, we use the following formula:
Daily recording size in GB ≈ total bitrate of all cameras (Mbps) × 10.8.
Required capacity in GB ≈ daily recording size × number of retention days × (1 + safety margin).
Example: four cameras averaging 2Mbps each means a total of 8Mbps, or about 86.4GB per day. Over 14 days we need about 1,210GB of video, and with a default 20% margin the need becomes about 1,452GB; so a 2TB drive can be considered after confirming the recorder supports that capacity. The 20% margin isn’t a fixed rule; it’s a practical reserve we may increase if filming conditions vary.
Practical table: four cameras recording continuously
The following table assumes four cameras running 24 hours, an average of 2Mbps per camera, and decimal marketing capacities for the drive (1TB = 1000GB). Results are approximate and don’t include all overhead data or space reserved by the recorder.
| Retention period | Approximate video size | With a 20% margin | Initial choice |
|---|---|---|---|
| 7 days | 605GB | 726GB | 1TB |
| 14 days | 1,210GB | 1,452GB | 2TB |
| 30 days | 2,592GB | 3,111GB | 4TB |
If the same cameras record at an average of 1Mbps per camera, the daily size drops to about 43.2GB. If the average rises to 4Mbps per camera, it becomes about 172.8GB per day. That’s why a 1TB drive may record for very different durations even with the same number of cameras.
When should I choose 500GB, 1TB, 2TB or 4TB?
500GB drive
May suit limited systems with a few cameras, intermittent motion recording, or short retention. In the four-camera example at 2Mbps each, 500GB theoretically holds about 5.8 days before the margin and any space used by the system, so it shouldn’t be assumed to cover a full week in these conditions.
1TB drive
A common initial choice for small systems with shorter archiving periods. In the previous four-camera example it theoretically holds about 11.6 days before margins. If you need a guaranteed 14 days in the same conditions, don’t rely on 1TB alone.
2TB drive
Gives more space for a home or shop system with several cameras, and may cover needs of about two weeks in the four-camera example with a reasonable margin. But higher-bitrate cameras may shorten the period, so calculate the need from the real settings rather than relying on the capacity’s marketing name.
4TB drive or larger
Initially suits those who need to keep recordings longer or have more cameras. In the four-camera example, 4TB gives an estimated capacity of about 30 days with a 20% margin, if all the space is usable and the bitrate stays close to the assumption. Always confirm the maximum supported per bay on the DVR or NVR.
Does H.265 save more space than H.264?
H.265/HEVC can usually deliver similar viewing quality at a lower bitrate than H.264/AVC, which may reduce drive space usage. But the saving isn’t fixed; it varies with the camera, lighting, motion and compression settings, and some devices offer additional enhanced codecs. Don’t rely on the “half the space” claim for every system: it’s better to compare the average Mbps after setting the quality you need, and to make sure the camera and recorder support the same codec.
Continuous recording or motion recording?
Continuous recording makes the calculation easier because the stream is stored all the time, and it lets you review what happened before motion was detected. Motion recording may reduce space usage when the site is quiet, but it depends on detection sensitivity, clip length and the amount of motion, and it may miss moments if the settings aren’t tuned well. Don’t automatically reduce the safety margin when enabling motion detection; monitor actual space usage over several days at peak times, then calculate based on that.
Why is a surveillance-specific drive preferred?
For systems running day and night, it’s better to choose a drive designed for continuous video recording workloads, not just any desktop drive available. Focus on the number of supported video streams, annual workload rate, endurance and the model’s actual warranty. For example, specialist companies like Seagate describe the SkyHawk line as optimised for 24/7 surveillance workloads; but each model’s specs and availability differ, and this doesn’t mean a specific product is currently available at Shaikh Alkar.
Also check the interface type (usually SATA), the drive size, the recorder’s maximum capacity, the installation location’s temperature and ventilation, and drive health alerts. On some systems space may be reserved for indexing or management files, and the available capacity will appear different from the number on the box.
Is RAID a substitute for backup?
No. Some RAID configurations reduce the chance of downtime when one drive fails, but they don’t protect against accidentally deleted recordings, recorder damage, fire or theft. If the footage is legally or operationally important, discuss a policy for exporting important clips and copying them to a separate location, and don’t rely on a single local copy.
Five steps before ordering a drive
- Write down the number of cameras, resolution, frame rate and recording method.
- Check the real average bitrate of each camera on the recorder.
- Decide how many days to keep and add a suitable margin.
- Check the maximum drive capacity the DVR or NVR supports and the required drive type.
- Calculate the size and test the actual retention period after installation; don’t rely on guesswork.
FAQ about CCTV drive capacity
How many days does a 1TB drive record for four cameras?
There’s no fixed answer; if each camera averages 2Mbps and recording is continuous, the theoretical average is about 11.6 days before the safety margin and system space. If the bitrate differs or motion recording is enabled, the result changes.
Can I know the number of recording days from 5MP resolution alone?
No. You need to know the bitrate, codec, frame rate and scene motion; two cameras with the same resolution can produce different amounts of data.
Is a regular computer drive suitable for a DVR?
Some regular drives may technically work, but for continuous use a drive designed for surveillance workloads is preferred, after confirming it’s compatible with the recorder.
What happens when recording space fills up?
On many DVR/NVR devices you can enable automatic overwriting of the oldest recordings, but this depends on the device settings. Check the Overwrite option and the retention policy, and don’t assume recordings will be kept forever.
Advice from the Shaikh Alkar team in Jordan
If you don’t know the right capacity, give us the number of cameras, their resolution or bitrate if available, the recorder type and the required retention period (7, 14 or 30 days). The Shaikh Alkar Satellite & Security Systems team will help you choose a balanced capacity without overspending, and check the drive’s compatibility, availability and current price before confirming the order. You can contact us or browse the surveillance systems section, and read the guide to choosing home security cameras and compare Wi-Fi and DVR.
Conclusion: The best drive isn’t always the biggest; it’s the one compatible with your device that provides the required recording time based on the actual bitrate with a reasonable safety margin. Do the calculation first, then check the available capacity and recording quality on the real system.
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Tell us how many cameras, where they’ll be installed and how long you need recordings kept, and we’ll help you pick a practical solution without unnecessary equipment.