‘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.
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). Modern H.265 compression roughly doubles the days you’d get versus older H.264.
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:
Setup
1TB
2TB
4TB
4 × 2MP cameras
~8–10 days
~16–20 days
~32–40 days
4 × 5MP cameras
~4–5 days
~8–10 days
~16–20 days
8 × 2MP cameras
~4–5 days
~8–10 days
~16–20 days
8 × 5MP cameras
~2–3 days
~4–5 days
~8–10 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.
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? It works, but surveillance-grade drives are built for 24×7 writing and last longer in a DVR/NVR. For continuous recording, they’re worth it.
What happens when the disk fills up? The recorder loops — it overwrites the oldest footage first, so you always keep the most recent days.
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.
