Related tools
Need only the total storage requirement? Use the CCTV Storage Calculator. Already know your installed HDD capacity? Calculate how many days it can record.
How NVR HDD Storage Is Calculated
The calculator uses configured bitrate, camera count, recording hours, retention days, and storage overhead. It converts Mbps to bytes over the selected recording period, then adds the planning overhead.
Recording seconds = days x recording hours/day x 3,600
Base storage = bitrate Mbps x 1,000,000 x recording seconds x cameras / 8
Required storage = base storage x (1 + overhead percentage / 100)
How Many HDDs Does My NVR Need?
Required capacity can be split across multiple HDD bays. This calculator recommends a practical equal-size drive configuration and does not force every bay to be filled when fewer drives can satisfy the requirement.
NVR HDD Bays Explained
NVRs may have 1 bay, 2 bays, 4 bays, 8 bays, or more. Supported disk count and maximum capacity vary by recorder model, so use the bay count and maximum drive size from the actual NVR specification.
HDD Capacity vs Usable Capacity
Advertised HDD capacities use decimal units. Recorder formatting, RAID, hot spares, reserved space, file-system behavior, and manufacturer-specific storage architecture can reduce usable recording capacity. This calculator assumes the listed HDD capacities are available as summed recording storage.
Surveillance HDD vs Desktop HDD
Surveillance-class HDDs are designed for continuous video-recording workloads and multi-stream environments. Desktop drives are not universally guaranteed to fail, but an NVR installation should use drives that match the recorder's compatibility list and workload requirements.
Why Bitrate Matters
Camera resolution alone does not determine storage. Actual storage depends strongly on configured bitrate, frame rate, image quality, scene complexity, codec, CBR/VBR settings, and recording behavior.
H.264 vs H.265
H.265 may allow lower bitrate under comparable settings, but actual storage savings are configuration-dependent. This calculator therefore uses the entered bitrate instead of applying a fixed codec multiplier.
Continuous vs Motion Recording
Continuous recording has predictable recording hours. Motion recording may reduce storage use, but actual savings depend on scene activity and cannot be reduced to one universal percentage.
Example NVR HDD Calculation
Sixteen cameras at 6 Mbps each recording 24 hours per day for 30 days need 31.104 TB before overhead. With 10% overhead, required storage is 34.2144 TB. With 2 HDD bays, the minimum listed equal-size configuration is 2 x 18 TB = 36 TB, if the NVR supports 18 TB drives.
FAQ
How much HDD storage does an NVR need?
It depends on camera count, configured bitrate, recording hours, retention days, and overhead. The calculator uses bitrate directly because resolution alone does not determine storage use.
What size HDD do I need for 8 cameras?
For 8 cameras at 4 Mbps each, 24 hours per day, 30 days, and 10% overhead, the estimate is about 11.4 TB, so a practical minimum from the listed sizes is 1 x 12 TB if the NVR supports that drive.
How many HDDs do I need for 16 CCTV cameras?
The number of HDDs depends on bitrate, retention, recording schedule, drive sizes, and NVR bay count. High-bitrate or long-retention systems may need multiple drives or a recorder with more bays.
Can I use two HDDs in an NVR?
Only if the NVR model supports two internal drives and the drive capacities are compatible. Check the recorder manufacturer's supported HDD list and maximum capacity per bay.
Do I need to fill every NVR HDD bay?
Not always. If one drive provides enough planned capacity and the recorder supports it, the calculator may recommend fewer drives than the available bay count.
Can I install different HDD sizes in an NVR?
Some recorders allow mixed drive sizes and some do not, especially with RAID or special storage modes. This calculator recommends equal-size configurations for simple planning.
Does H.265 reduce NVR storage use?
H.265 may allow lower bitrate under comparable settings, but savings are configuration-dependent. Use the bitrate configured in the camera or recorder when possible.
How long will a 4TB HDD last in an NVR?
It depends on the total recording bitrate and schedule. Use the CCTV Recording Time Calculator if you already know the installed storage capacity and want estimated retention.
What is the maximum HDD size an NVR supports?
There is no universal maximum. It depends on the recorder model, firmware, interface, and manufacturer compatibility list.
Does RAID reduce usable CCTV storage?
RAID, hot spares, recorder-reserved space, and file-system behavior can reduce usable recording capacity. This calculator does not model RAID in this phase.
Should I use a surveillance HDD in an NVR?
Surveillance-class HDDs are designed for continuous video-recording and multi-stream workloads. Desktop drives are not universally guaranteed to fail, but compatibility and workload suitability should be checked.
Planning note
Verify the NVR's supported HDD models, maximum capacity per bay, interface requirements, firmware compatibility, RAID behavior, and usable-capacity configuration before purchasing drives.