Why bitrate, scene and codec drive actual storage use.
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How Long Will a 2 TB NVR Record Four Cameras? Calculator + Examples
How many days can a 2TB NVR record with four 4K cameras? Use camera count, measured bitrate and usable storage to calculate 24/7 recording retention realistically.
THE ANSWER FIRST
What homeowners need to know.
It depends on average bitrate, not just the '4K' label. At an illustrative, constant 4 megabits per second (Mbps) per camera, four cameras together consume about 172.8 decimal GB per day. A nominal 2,000 GB drive would therefore hold about 11.6 days before filesystem overhead, reserved space, additional streams and variable bitrate. At 8 Mbps per camera, it would be about half as long.
RECORDING RETENTION IS A MATH PROBLEM
A 2 TB label is not a number of recording days
| Average bitrate per camera | Four-camera storage per day | Nominal 2 TB retention* |
|---|---|---|
| 2 Mbps | 86.4 GB | 23.1 days |
| 4 Mbps | 172.8 GB | 11.6 days |
| 6 Mbps | 259.2 GB | 7.7 days |
| 8 Mbps | 345.6 GB | 5.8 days |
*Table uses four always-recording cameras and a nominal decimal 2 TB capacity with no overhead allowance. It is calculated, not measured. Your real retention will vary.
EXPLANATION WITHOUT THE HYPESTEP 01 STEP 02 STEP 03 STEP 04 STEP 05
Understand the real trade-offs.
The formula to estimate NVR recording days
One Mbps is one million bits each second. Divide by eight to convert bits to bytes; multiply by 86,400 seconds per day. This produces approximately 10.8 decimal gigabytes per day for every continuous 1 Mbps of video.
Daily GB = camera count × Mbps per camera × 10.8 × recording duty fraction. Estimated days = usable disk GB ÷ daily GB. Use a conservative usable-capacity margin rather than treating every advertised drive byte as writable footage.
Why '4K' does not give you a single bitrate
Resolution describes pixel dimensions; storage depends on codec, frame rate, quality, scene movement, night conditions, audio, extra streams and bitrate controls. A quiet driveway at night and a busy street in daytime can produce very different average rates.
Axis Communications emphasizes dimensioning storage by bitrate and workload, not simply by megapixel count. Use measured camera bitrates from your recording settings or vendor storage calculator where possible.
Check whether you're recording 24/7 or only events
A wired PoE NVR can often record continuously, so a 100% duty fraction is a useful planning assumption. A battery camera that records motion events does not follow the same retention estimate unless you know how much time it is actually recording.
Do not reduce a 24/7 plan to a tiny duty fraction just to obtain an attractive retention figure. For investigations, continuous video may matter more than the convenience of conserving disk space.
Keep spare capacity and consider drive failure
Drive manufacturers describe capacity in decimal units, while operating systems can display binary units. Filesystem overhead, reserved capacity, NVR operating files, event indexes and non-video data can further reduce available space. RAID mirroring can reduce usable capacity if you add disks.
A NVR hard drive is not a substitute for an off-device backup of important clips. Test that you can export footage, access timestamps and recover video after an outage. A two-drive setup does not automatically provide redundancy unless configured for it.
How to choose between 2 TB and a larger disk
Start with the minimum number of days you actually need, then work backward from measured average bitrate per camera. For example, with four cameras at 4 Mbps and a 20% planning reserve, 30 days of footage would require roughly 6.5 TB of nominal disk capacity under those simplifying assumptions.
Confirm supported disk sizes and bay count with the exact NVR model, then allow for growth when adding cameras. Avoid buying an unsupported drive solely because it appears cheaper per terabyte.
FOXYPICK DECISION HELPER
Calculate your own storage retention
Explore a transparent starting point, then check the full research and your actual product requirements.
24/7 recording at a constant assumed average bitrate. Actual retention varies; this is not a hardware guarantee.
CHECK THE ORIGINAL MATERIALAxis Communications: Video compression and storage ↗ TP-Link: 24/7 CCTV storage calculation ↗ Axis: Surveillance storage examples ↗
Evidence, not manufactured testing.
The facts and formulas above are grounded in the linked technical material. FoxyPick has not performed comparative laboratory testing of all the products discussed.
Confirms the Mbps × 10.8 GB/day conversion.
Illustrates how retention depends on compression, stream and bitrate.
QUESTIONS WORTH ANSWERING
Frequently asked before buying.
How many days does 2 TB hold for four 4K cameras?
If the actual average bitrate is 4 Mbps per camera and recording is continuous, the nominal calculation is about 11.6 days before capacity allowances. 4K itself does not specify bitrate.
Will H.265 double my recording days?
Not necessarily. Codec benefits depend on scene, device settings and implementation; use observed bitrates rather than a blanket promise.
Does motion recording make a drive last longer?
Often, but retention cannot be accurately estimated without the actual recorded-time fraction and clip behavior.
How can I get more retention?
Adjust recording quality or motion policy when acceptable, add compatible storage, choose more efficient compression if supported, or reduce simultaneous recording streams.
CONTINUE YOUR RESEARCH
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Disclosure: FoxyPick may earn commissions from eligible affiliate links elsewhere on the site. The founder operates a Phoenix-area wall panel business. These connections do not make untested product performance claims true. See disclosures.
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