‘How many days will it record?’ is the question every CCTV buyer asks about a hard disk — and the honest answer is ‘it depends’. It depends on your camera count, resolution, and recording settings. Here’s a clear chart and the simple maths behind it, so you can pick the right disk size with confidence.
Table of Contents
What decides your recording days
Three things: how many cameras (more cameras fill the disk faster), resolution (a 4K camera uses far more space than a 2MP one), and recording mode (continuous 24×7 uses more than motion-only). H.265 can reduce storage compared with H.264 at similar perceived quality, but the gain varies by scene, recorder, camera and bitrate settings.
How to calculate CCTV storage
Start with the average bitrate for every camera. Add those bitrates, convert from bits to bytes, then multiply by the number of seconds in the retention period. Recorder manufacturers often provide calculators, but the basic planning formula is:
Add a safety margin for disk formatting, bitrate peaks and changing scenes.
Example: four 2MP cameras for 14 days
If each camera averages 1.5 Mbps, the combined bitrate is 6 Mbps. The estimate is 6 × 10.8 × 14 = about 907 GB before allowing for formatting and variation. That makes 1TB a close planning fit under those assumptions; higher bitrate or longer retention requires more capacity.
Do not use resolution alone to calculate storage. Two cameras with the same resolution can have very different bitrates because of frame rate, image complexity, codec, quality settings and night noise.
Approximate recording days by disk size
These are realistic estimates for continuous 24×7 recording on H.265. Your exact numbers vary with settings, but this is a reliable planning guide:
These are estimates, not fixed numbers — storage depends heavily on bitrate. Figures assume continuous 24×7 recording, H.265+ / smart codec, and typical average bitrates (2MP ≈ 1.5 Mbps, 5MP ≈ 3 Mbps, 4K ≈ 6 Mbps) on ~93% usable disk. Busy, high-motion scenes or maximum-quality recording can cut these by up to half.
| Setup | 500GB | 1TB | 2TB | 4TB |
|---|---|---|---|---|
| 4 × 2MP | ~7 days | ~14 days | ~29 days | ~57 days |
| 4 × 5MP | ~4 days | ~7 days | ~14 days | ~29 days |
| 4 × 4K (8MP) | ~2 days | ~4 days | ~7 days | ~14 days |
| 8 × 2MP | ~4 days | ~7 days | ~14 days | ~29 days |
| 8 × 5MP | ~2 days | ~4 days | ~7 days | ~14 days |
| 8 × 4K (8MP) | ~1 day | ~2 days | ~4 days | ~7 days |
| 16 × 2MP | ~2 days | ~4 days | ~7 days | ~14 days |
| 16 × 5MP | ~1 day | ~2 days | ~4 days | ~7 days |
Notice the pattern: doubling the resolution roughly halves the days, and doubling the cameras does the same. If you want a specific retention window — say two weeks — work backwards from this chart to your disk size.
How to get more recording days
You don’t always need a bigger disk. You can enable motion-only recording (records only when something moves — can multiply your days), use H.265 compression if your recorder supports it, or lower the frame rate slightly on less-critical cameras. Combine these and a 2TB disk can stretch surprisingly far. But if you simply want more history, a bigger disk is the clean solution.
Continuous vs motion recording
Continuous recording gives a predictable timeline but uses storage at all times. Motion recording can extend retention in quiet areas, yet the result depends on how often motion is detected and whether pre-record and post-record buffers are enabled. A busy road, trees in wind or video noise at night can produce far more events than expected.
For important entrances, some users choose continuous recording at a moderate frame rate and event markers for fast searching. Test the real system for several days, then compare the oldest available footage with the required retention window.
Hard-disk selection checklist
- Check the DVR/NVR maximum capacity per bay and number of supported bays.
- Choose a drive intended and warranted for the expected recording workload.
- Allow capacity headroom instead of sizing to an exact theoretical result.
- Enable disk-health, recording-failure and storage-full notifications where supported.
- Verify playback from every camera after installation and periodically afterward.
Preserve important footage before it is overwritten
Loop recording can remove the oldest video automatically. When an incident occurs, export the relevant time window promptly to separate storage and verify that the exported file plays correctly. Keep the recorder’s date and time accurate so footage can be located reliably.
New or refurbished — and which brand?
For a hard disk that runs 24×7, reliability matters. We stock both brand-new sealed drives and professionally tested refurbished drives for maximum value — browse CCTV hard disks in the store. Seagate and WD are the trusted names; for very heavy multi-camera loads, ask us about surveillance-grade drives built for continuous writing.
Match storage to your system
Storage is one piece of the puzzle. If you’re still planning cameras and resolution, see our resolution guide and camera-count guide first — those decisions drive your disk size.
Frequently asked questions
Can I use a normal desktop hard disk?
A compatible desktop drive may function, but surveillance-rated drives are designed and workload-rated for continuous multi-stream recording. Check the recorder compatibility list, workload and warranty terms before choosing.
What happens when the disk fills up?
Most recorders can be configured to overwrite the oldest footage when storage is full. Confirm that overwrite is enabled and check disk-health alerts, because settings vary.
Can I add a second hard disk?
Many IP NVRs and larger DVRs support two or more disks. Check your recorder’s bays — we can confirm for your model.
Tell us your camera count and how many days you want to keep, and we’ll recommend the exact disk. Browse options in our store.
After estimating retention, compare CCTV DVR prices and storage options by channel count, SATA bays, recording quality and camera compatibility.
Storage Planning by Recorder Size
Retention requirements rise with camera count, bitrate and recording schedule. Compare the storage-bay and maximum-capacity specifications of 8 channel, 16 channel and 32 channel NVRs before selecting a hard disk. For a complete wired package, check whether storage is included in the chosen 5MP HD CCTV combo.
Check Storage Inside a Complete CCTV Package
When comparing CCTV camera packages with storage, verify the included hard-disk capacity and the exact recorder’s supported limit. Camera count, resolution, bitrate and recording schedule determine whether two similarly priced sets provide the same retention.
For a CP Plus system, use this estimate before comparing CP Plus CCTV cameras and recorders; confirm the exact DVR or NVR drive-capacity limit on its product page.
For WiFi or IP cameras that record directly to removable storage instead of a DVR or NVR hard disk, compare current CCTV camera memory card prices and confirm the camera-supported microSD capacity.
