CCTV storage calculatorHow long will your footage last before it overwrites?
A free, instant NVR and DVR recording time calculator for 4K CCTV. Pick a hard drive size and your camera count and the days of footage you will keep drop out below. Sizing for 1080p, motion-only or DVR systems is covered in the notes underneath.
Retention
13days
Based on 4K H.265, 24/7 continuous recording (~77 GB per camera per day). Motion-only recording will stretch this considerably.
How the maths works
A single 4K camera recording 24/7 in H.265 chews through roughly 77 GB a day. That works out to about 12.9 camera-days per terabyte. So three cameras on a 1 TB drive lasts a touch over four days before the recorder starts overwriting the oldest footage. Add cameras and retention drops; bump the drive size and retention climbs in a straight line.
The shorthand we use on a site survey:
Days ≈ (TB × 12.9) ÷ cameras
Most domestic installs sit comfortably at 7 to 14 days of retention. Anything beyond a fortnight is overkill for a typical home: if something happens, you tend to know within a day or two and pull the footage long before it rolls. Where longer retention matters is commercial sites, properties with no neighbours overlooking, or anywhere a quiet incident might not be spotted for a week.
Common scenarios
A few of the combinations we install most often, so you can see what falls out at typical drive sizes.
| Cameras | Hard drive | Days retention |
|---|---|---|
| 3 | 4 TB | 17 days |
| 3 | 8 TB | 34 days |
| 4 | 4 TB | 13 days |
| 4 | 8 TB | 26 days |
| 6 | 8 TB | 17 days |
| 6 | 16 TB | 34 days |
| 8 | 16 TB | 26 days |
| 8 | 24 TB | 39 days |
Things that change the number
The figure above assumes a fixed setup: 4K resolution, H.265 compression, and continuous 24/7 recording. Real installs vary on a few axes:
- Motion-only recording. Recording only when something moves can cut storage use by half or more on quiet sites. The trade-off is that you lose the constant timeline, which sometimes matters when piecing together a sequence.
- Frame rate. Dropping from 25 fps to 15 fps cuts bitrate roughly in half. Most domestic CCTV is recorded at 15 fps because the footage is still smooth enough to identify faces and number plates.
- Scene activity. H.265 compresses static scenes very efficiently. A back garden that barely moves uses far less storage than a busy frontage facing a main road.
- Drive headroom. NVR drives are never run to 100% full. Plan for 80–90% usable to keep the recorder happy long-term.
If you want a system spec'd around a specific retention target (a fortnight is the usual ask), we'll size the drive accordingly during the site survey. The NVR recorder we fit takes drives up to 24 TB without fuss. If you'd rather we worked the retention out for you on site, you can book a free CCTV site survey in Leicester. One fixed price for the whole job, drive included, and the price we quote is the price you pay.
How CCTV storage works
Every CCTV camera produces a continuous video stream, and every stream has a bitrate measured in megabits per second. Multiply that bitrate by the number of seconds in a day, then by the number of cameras, then by the number of days you want to keep, and you have the total storage your NVR (or DVR) needs. The four numbers that decide the answer are bitrate, hours per day recorded, retention days and camera count.
For a working baseline, a single 4K H.265 camera on 24/7 continuous recording averages around 77 GB per day. Drop to 1080p H.265 and the same camera sits closer to 35 to 40 GB per day. The calculator at the top of the page uses the 4K continuous figure because it's the worst case for most modern CCTV cameras we install. Anything else is going to land cheaper.
What "storage capacity in days" actually means
Storage capacity in days, or retention, is how many days of footage your NVR will hold before it starts overwriting the oldest clips. NVRs run on a rolling loop: when the drive fills, the recorder doesn't stop, it overwrites frame by frame. Planning retention is mostly a question of how long you'd realistically need to go back. For a home, a fortnight is the standard ask. For a business or a quiet site with no overlooking neighbours, four to six weeks is more sensible.
The three factors that move the number
- Resolution. The dominant lever. 4K (8 MP) is roughly double the storage of 1080p (2 MP) on the same compression. 5 MP and 4 MP cameras sit in between. If retention is tight, dropping a couple of cameras to 1080p on scenes that don't need the extra detail buys you a lot of headroom.
- Frame rate. Most CCTV is recorded at 15 fps because the footage is still smooth enough to read faces and number plates. Going to 25 or 30 fps roughly doubles the bitrate without much practical benefit for evidence capture.
- Recording mode. Continuous 24/7 is the baseline. Motion-only recording can cut storage by half or more on quiet sites: a back garden that barely moves uses a fraction of what a busy frontage on a main road uses. The trade-off with motion-only is that you lose the unbroken timeline, which sometimes matters when piecing together a sequence.
NVR vs DVR: why the calculator skews modern
DVR (Digital Video Recorder) is the older analogue format. It records over coaxial cable, usually caps at 1080p, and uses H.264 compression. NVR (Network Video Recorder) is the modern IP and PoE format, supports 4K and beyond, and uses the more efficient H.265 codec. The maths is identical between the two, but per-camera bitrates on NVR are higher because the resolution is higher. If you're running a DVR-era 1080p system on H.264, expect daily storage per camera in the 25 to 35 GB range, and use the calculator above as an upper bound rather than a literal figure. For a deeper breakdown of what each spec line on a camera actually means, our CCTV specs cheat sheet walks through resolution, bitrate, codecs and frame rate one at a time.
Typical storage for common setups
A few real-world combinations we size for regularly:
- 4 cameras, 1080p, motion-only, 30 days: 2 to 4 TB is comfortable.
- 4 cameras, 4K, continuous, 30 days: 9 to 10 TB. Drop to motion-only and a 4 TB drive can hit the same retention.
- 6 cameras, 4K, continuous, 14 days: 8 TB lands close. The 16 TB row in the table above gives a margin.
- 8 cameras, 4K, continuous, 30 days: 16 to 24 TB depending on scene activity. This is the territory where commercial sites usually sit.
Hard drive sizing rules of thumb
- Never run an NVR drive to 100% full. Plan for 80 to 90% usable to keep the recorder healthy long-term and leave headroom for the index.
- Use surveillance-rated drives (the WD Purple and Seagate SkyHawk ranges are the two we see most). Desktop drives aren't built for the 24/7 write workload and fail early.
- One large drive beats two smaller ones in most domestic NVRs. Fewer moving parts, simpler RAID configuration if you ever add redundancy.
- Round up. If the calculator lands you at 13.4 days on a 4 TB drive and you want a fortnight, fit the next size up rather than running on the line.
When we spec a system on a home CCTV installation, we work backwards from the retention figure the customer wants, not forwards from a drive size. It's the only sensible way round.
CCTV storage FAQ
How much storage does CCTV need?
A 4K camera recording 24/7 in H.265 uses roughly 77 GB a day, which works out to about 12.9 camera-days per terabyte. A typical 4-camera 4K install on a 4 TB drive lands at around 13 days of retention. Drop to 1080p, switch to motion-only or lower the frame rate and the same drive stretches considerably further.
How long does CCTV footage last before it overwrites?
Until the drive fills up. NVRs run on a rolling loop, so once the disk is full the oldest footage is overwritten frame by frame as new footage comes in. Most domestic installs are sized for 7 to 14 days of retention. We cover this in more detail in our FAQ on how long CCTV footage lasts before it overwrites.
How do I calculate NVR storage?
Multiply the per-camera daily bitrate by the number of cameras and the number of days you want to retain. The shorthand for a 4K H.265 continuous setup is: days ≈ (drive TB × 12.9) ÷ cameras. For 1080p H.265 the figure roughly doubles. For motion-only it can double again on quiet sites.
Is 1 TB enough for CCTV?
For one or two 1080p cameras recording on motion, 1 TB is plenty and will easily give a fortnight of retention. For a 4-camera 4K continuous setup, 1 TB lands at around three days, which is usually too tight. Most 4-camera installs we fit start at 4 TB.
How many days of CCTV footage can I store?
It depends on resolution, frame rate, recording mode and how many cameras share the drive. Use the calculator at the top of this page for a 4K continuous baseline, then expect the real-world figure to be 1.5x to 3x longer once motion-only and scene compression are factored in.
What is the difference between NVR and DVR storage?
DVR is the older analogue format that records over coaxial cable, usually capped at 1080p. NVR is the IP and PoE format used by modern systems, supports resolutions up to 4K and beyond, and uses the more efficient H.265 codec. The maths is the same, but NVR cameras typically push a higher bitrate per stream so storage planning matters more.
Does 4K CCTV use more storage than 1080p?
Yes, roughly twice as much. A 4K H.265 camera averages around 77 GB per day on continuous recording. The equivalent 1080p H.265 camera sits closer to 35 to 40 GB per day. Frame rate and scene activity move the figure in either direction.
How big a hard drive do I need for 30 days of CCTV footage?
For 4 cameras at 4K continuous, you need roughly 9 to 10 TB for a clean 30-day retention. Drop to 1080p continuous and 4 TB is enough. Switch to motion-only on quiet scenes and 4 TB can stretch to 30 days at 4K. The calculator above gives you a continuous-recording baseline to size from.
Want this dialled in for your property?
We visit, map the blind spots, and quote one fixed price on the spot.