CCTV Storage Calculator
Working out how big a hard drive your CCTV system needs comes down to camera count, resolution, frame rate, video quality, compression and how long you need to keep the footage. This calculator does the maths for you and points you to a real WD Purple or Toshiba S300 drive that fits — both genuine UK stock, both built for continuous surveillance recording rather than desktop use.
Build your estimate
Estimated storage needed
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| Per camera, per day | – |
| All cameras, per day | – |
| Over your retention period | – |
Recommended drives
How the calculation works
The calculator starts from a typical bitrate for each resolution at 25fps and medium quality, recording in H.265 — the same baseline figures we use on our surveillance hard drives page — then scales that up or down for the frame rate and video quality you pick, adjusts for the compression format, and multiplies by how many hours a day the camera actually records and how many days you need to keep the footage. Motion and AcuSense event recording only writes data when something is happening, which is why it dramatically reduces the total compared with continuous recording, but the exact saving depends on how much activity a site actually has, so treat the "typical" and "quiet site" options as estimates either side of the real figure.
This follows the same broad approach as manufacturer and distributor tools like the WD surveillance capacity calculator and Norbain's CCTV storage calculator — camera count, resolution, frame rate, quality and compression are the standard inputs across the industry. Every site is different, though, so we always recommend rounding up to the next drive size rather than cutting it fine.
Why WD Purple and Toshiba S300?
Standard desktop hard drives are built to spin for a few hours a day. A CCTV recorder writes to its drive every second of every day from every camera at once — a completely different workload. WD Purple and Toshiba S300 drives are both built specifically for that continuous, multi-stream write load, which is why they last where a desktop drive drops frames or fails within a year. Both ranges work in HiLook, Hikvision and Dahua NVRs and DVRs. See the full range and a plain-English buying guide on our surveillance hard drives page.
FAQs
I've heard 1TB covers 30 days on an 8MP camera. Is that true?
Only for motion-triggered recording, not continuous. At a typical 25 to 30fps recording continuously, 24/7, an 8MP camera in H.265 actually needs closer to 2 to 2.5TB for 30 days — figures vary quite a bit across online sources depending on exactly what bitrate and frame rate they assume, which is part of why the "1TB" rule of thumb gets repeated so widely without much context. Set the Recording Mode above to "Motion / AcuSense event only" and the same setup lands right around 1TB, which is where that figure most likely comes from. Continuous is the safer assumption if you are not certain how the recorder will end up configured.
How accurate is this calculator?
It gives a solid estimate based on typical bitrates, but actual file sizes vary with scene complexity, lighting and the specific camera model. We always recommend rounding up to the next drive capacity rather than sizing exactly to the estimate — footage you need is exactly the footage a full drive overwrites first.
What frame rate and video quality should I choose?
25 to 30fps at medium to high quality is standard for most installations and is what we default to above. Lower frame rates such as 12 to 15fps reduce storage needs and are often adequate for general observation, but can miss fast-moving detail such as vehicle number plates or someone moving quickly through frame.
Should I choose continuous or motion recording?
Continuous recording is the safer choice if you need a complete record of everything, and it is what most commercial sites use. Motion or AcuSense event recording can cut storage needs considerably on quieter sites, but a very active scene — a busy car park, a road-facing camera — will trigger far more often than the "typical" setting assumes.
What if my estimate falls between two drive sizes?
Round up. A drive that fills early simply overwrites your oldest footage, which tends to be exactly the footage an investigation needs weeks later.
Can I mix WD Purple and Toshiba S300 drives in the same recorder?
Yes — most NVRs and DVRs with multiple bays do not require drives to match, though we would not recommend mixing capacities in a RAID array. For a single-bay recorder, either brand works equally well.
Do I need a different drive for IP cameras versus HD-TVI coax cameras?
No — the drive sits inside the recorder either way and does not care whether the cameras are IP or coax. What changes is the recorder itself: an NVR for IP/PoE cameras, a DVR for HD-TVI. See our NVRs and DVRs.
Not sure which recorder or camera count fits your site? Our Wolverhampton trade counter and showroom can talk it through, or browse the full surveillance hard drive range.