Security Camera Storage Calculator: Cameras, Bitrate and Days

The short answer

To estimate security-camera storage, multiply the total camera bitrate by the recording time and retention period, then convert bits to bytes:

Storage (GB) = Cameras × Bitrate (Mbps) × Recording seconds × Retention days ÷ 8 ÷ 1,000

For continuous recording, the shortcut is:

Storage per day (GB) = Cameras × Bitrate (Mbps) × 10.8

Then:

Storage (decimal TB) = Cameras × Bitrate (Mbps) × 10.8 × Retention days ÷ 1,000

Adjust the result for the percentage of each day that is actually recorded, audio, system overhead, snapshots, filesystem overhead, and the capacity lost to RAID. The result is a planning estimate—not the exact free space shown by a particular NAS.

If you are ready to compare hardware, Browse NAS options based on the capacity, drive bays, network connections, and surveillance software you need.

Inputs for the calculator

A useful estimate needs more than the camera resolution. Gather these inputs first:

Input	What to record	Why it matters
Camera count	Number of streams being recorded	Storage and write traffic scale approximately linearly
Average bitrate	Mbps per camera, preferably the actual average VBR bitrate	Bitrate determines storage more directly than resolution
Codec	H.264, H.265, or another supported codec	The codec affects the bitrate needed for a given image quality; it does not change the storage math once bitrate is known
Recording schedule	Continuous, scheduled, or motion-triggered	A camera recording for 12 hours does not use the same capacity as one recording 24/7
Retention	Number of days or hours to keep	Capacity increases linearly with retention
Audio	Whether audio is recorded and its bitrate	Audio adds to the stream bitrate
NAS overhead	Filesystem, metadata, snapshots, recycle bins, and application data	Not all installed disk capacity is available for recordings
RAID layout	RAID level, ZFS vdev design, or another storage layout	Usable capacity is lower than the sum of the installed drives

Use the camera or VMS's average recorded bitrate when possible. A setting such as “4K” or “8 MP” does not provide enough information by itself. Two cameras with the same resolution can use different bitrates because of frame rate, image complexity, codec, keyframe interval, quality settings, and scene activity.

Average versus maximum bitrate

Variable-bitrate recording can produce very different results depending on the scene:

• A quiet indoor scene may use less storage than its configured maximum.
• Foliage, rain, crowds, traffic, and changing shadows can increase bitrate.
• Night scenes can be demanding because of noise and motion.
• A camera's advertised bitrate range is not the same as its actual average.

For a first estimate, use the configured average or a measured average from the camera system. For a high-consequence installation, size against a conservative value and validate it with several days of real recordings.

The security-camera storage formula

Full formula

Start with bitrate in megabits per second:

Storage (GB) = Camera count × Bitrate (Mbps) × Recording seconds × Retention days ÷ 8 ÷ 1,000

For 24-hour recording:

Recording seconds per day = 86,400

Therefore:

Storage per camera per day (GB) = Bitrate (Mbps) × 86,400 ÷ 8 ÷ 1,000

Which simplifies to:

Storage per camera per day (GB) = Bitrate (Mbps) × 10.8

The complete 24/7 shortcut is:

Storage (decimal TB) = Camera count × Bitrate (Mbps) × 10.8 × Retention days ÷ 1,000

This uses decimal units:

• 1,000 MB = 1 GB
• 1,000 GB = 1 TB

Drive manufacturers generally label capacity in decimal units, while operating systems may display capacity differently. Use one unit system consistently when comparing the estimate with the NAS interface.

Recording schedules and motion detection

Apply a recording factor when streams are not recorded continuously:

Adjusted storage = Continuous storage × Recording factor

Examples:

• 24/7 recording: factor 1.0
• 12 hours per day: factor 0.5
• 6 hours per day: factor 0.25

Motion recording is harder to predict. If cameras record motion for an average of 35% of the day, use 0.35 as a starting estimate:

Motion-adjusted storage = 24/7 storage × 0.35

This is an average, not a guarantee. If retention is a security requirement, consider sizing for busy periods rather than relying only on a low motion percentage.

Add a planning allowance

The bitrate calculation represents recorded media only. Capacity is also consumed by filesystem structures, surveillance indexes, thumbnails, event data, snapshots, NAS applications, and free-space requirements.

Add a planning allowance after calculating the recording total:

Planned capacity = Calculated recording capacity × (1 + allowance)

For example, a 15% allowance uses a multiplier of 1.15. The appropriate allowance depends on the NAS filesystem, surveillance application, snapshot policy, and how much free space you want to preserve. Do not treat a planning allowance as a replacement for checking the specific NAS and software.

Worked example

Assume:

• 16 cameras
• 6 Mbps average bitrate per camera
• Continuous recording
• 30-day retention
• No audio counted separately
• 15% planning allowance

First calculate the daily storage:

16 × 6 × 10.8 = 1,036.8 GB per day

Then calculate 30-day storage:

1,036.8 × 30 = 31,104 GB

Convert to decimal terabytes:

31,104 ÷ 1,000 = 31.104 TB

Add the planning allowance:

31.104 × 1.15 = 35.7696 TB

The planning result is therefore approximately 35.8 TB of usable recording capacity before accounting for the specific RAID layout and any additional NAS data.

If the same cameras record for an average of 50% of each day:

35.7696 × 0.5 = 17.8848 TB

This illustrates why recording policy can matter as much as camera count. However, motion recording should be validated against real activity and the required evidence-retention policy.

Codec, frame rate, and image quality

The storage formula only needs the final bitrate. Codec and camera settings matter because they determine that bitrate.

H.264 versus H.265

H.265 may reduce bitrate for comparable image quality in some systems, but the actual result depends on the camera, scene, settings, and whether the recorder can decode or process the stream. Do not reduce your storage estimate merely because a camera supports H.265. Use the bitrate produced by the chosen recording profile.

Compatibility also matters. A camera, NVR, NAS application, or client may not support every codec or hardware-accelerated decode path. Confirm the recording software's support before committing to a codec-specific design.

Main stream and substream

Many cameras provide:

• A high-quality main stream for recording
• A lower-bandwidth substream for live grids or remote viewing

The substream can reduce viewing bandwidth and client workload, but it does not reduce storage if the main stream is what the NAS records. Determine which stream the surveillance application actually saves.

Audio and extra streams

If audio is recorded separately, add its bitrate to the video bitrate before using the formula:

Total bitrate = Video bitrate + Audio bitrate

Additional streams, snapshots, analytics clips, or event exports may require capacity beyond the primary continuous recording estimate.

Write workload and network throughput

Storage capacity answers “how many days?” It does not answer whether the NAS can reliably receive and write all camera streams.

Aggregate camera bandwidth

Calculate the incoming stream rate:

Aggregate bandwidth (Mbps) = Camera count × Average bitrate (Mbps)

For the worked example:

16 × 6 Mbps = 96 Mbps

Convert a network rate to a rough byte rate with:

Bandwidth (Gbps) / 8 = theoretical GB/s

Or, for megabits per second:

Bandwidth (Mbps) / 8 = theoretical MB/s

Therefore:

96 Mbps / 8 = 12 MB/s

This is the camera payload only. Network protocol overhead, encryption, management traffic, live viewing, backups, and other NAS users require additional headroom. Check the complete path:

• Camera network or PoE switch
• Uplink to the NAS
• NAS network interface
• Virtual switch or bonded interface, if used
• Surveillance application and storage pool

A camera installation can fail because of a congested uplink even when the disks have plenty of capacity.

Write workload

Continuous surveillance is generally a sustained write workload made up of multiple streams. The NAS must handle:

• Concurrent writes from all active cameras
• File rotation and retention deletion
• Recording indexes and event metadata
• Motion or object-detection events
• Playback reads while recording continues
• Snapshots, replication, or backups
• Other NAS services such as file sharing or media streaming

Do not choose a NAS based only on the advertised network port speed. Verify the surveillance application's camera limit, supported protocols, storage recommendations, filesystem support, and any documented performance guidance. Exact camera capacity cannot be inferred responsibly without the NAS model, application, recording settings, and workload.

RAID and usable surveillance capacity

RAID changes usable capacity, redundancy, and failure behavior. It does not change the bitrate formula.

For a rough matched-drive estimate:

• RAID 0: approximately the sum of all drives, with no drive-failure protection
• RAID 1: approximately the capacity of one drive in a mirrored pair
• RAID 5: approximately (number of drives - 1) × smallest drive
• RAID 6: approximately (number of drives - 2) × smallest drive
• RAID 10: approximately half of the combined raw capacity with matched drives

These are planning approximations. Actual usable space is affected by drive size, filesystem formatting, RAID implementation, reserved space, and storage-pool design.

With ZFS, do not assume that every pool layout has the same usable-capacity formula. RAIDZ level, vdev width, ashift, record settings, pool reservations, snapshots, and the number of vdevs all affect the result. Calculate the recording requirement first, then select a ZFS layout that provides the desired redundancy and expansion path.

RAID is not backup

RAID can keep a storage pool available after certain drive failures. It does not protect against:

• Accidental deletion
• Ransomware
• Corrupt recordings
• Fire, theft, or flood
• A failed NAS or controller
• Incorrect retention or deletion policies
• A problem replicated to every copy

A surveillance system should have a separate plan for important footage. Depending on the risk and retention requirements, that may include a second NAS, removable storage, cloud archival, or exported incident footage. Test that recordings can actually be restored and played back.

RAID also consumes capacity, so use usable post-RAID capacity—not the total label capacity of the installed drives—when comparing the array with the calculator result.

NAS versus NVR: which role does each device perform?

A NAS and an NVR can overlap, but they are not automatically interchangeable.

Dedicated NVR

A dedicated NVR commonly provides:

• Camera discovery and authentication
• Recording schedules
• Motion and event handling
• Camera management
• Playback and timeline search
• Alerts and user permissions
• A storage interface designed around surveillance

Some NVRs use internal disks, while others can record to external or network storage. Compatibility, licensing, supported camera protocols, and storage limits vary.

NAS-based surveillance

A NAS can host a surveillance application or provide storage to an NVR. It may also offer:

• General file storage
• Backup targets
• Media serving
• Virtual machines or containers
• Snapshots and replication
• Centralized user management

The trade-off is configuration and validation. Check whether the chosen surveillance software supports your cameras, codec, event features, retention policy, and intended storage protocol. Do not assume that any camera can record directly to any NAS simply because both support network file sharing.

Hybrid design

A hybrid design can place camera management and event processing on an NVR while using a NAS for longer retention or secondary copies. This can be useful when local NVR capacity is limited, but it adds network traffic and another failure point. Define which device is the primary recording source and which copy is used for backup or extended retention.

Drives, SSD cache, power, and expansion

Drives for surveillance

Surveillance storage is a sustained-write workload. Select drives that are supported by the NAS and appropriate for the expected workload, vibration environment, duty cycle, and RAID or ZFS design. Do not mix drive types or capacities casually; the usable result may be limited by the smallest drive, and vendor compatibility policies may apply.

Drive choice also affects:

• Raw capacity and future retention
• Rebuild time and risk exposure
• Noise and power consumption
• Vibration in multi-drive enclosures
• Warranty and workload suitability
• Expansion options

Exact drive endurance, compatibility, and performance must be checked against the specific NAS and drive models.

Is SSD cache necessary?

SSD cache is not automatically useful for camera recording. Surveillance writes are often sustained and sequential, so cache may not add meaningful capacity or reliable throughput. It can also introduce cost, endurance considerations, and another component to monitor.

Consider SSD cache only when the NAS documentation and measured workload show a clear benefit, such as mixed surveillance and general file workloads. It does not replace a larger recording pool, adequate RAM, a suitable network, or a backup plan.

Power and expansion

A surveillance NAS runs continuously. Account for:

• NAS and drive power draw
• PoE switch power budget
• UPS capacity and runtime
• Safe shutdown behavior
• Cooling and drive temperatures
• Space for additional drives
• Whether the storage pool can be expanded in the desired way

Expansion is not universal. Some systems add drives one at a time, some expand by replacing drives, and ZFS pools commonly require careful vdev planning. Confirm the supported expansion method before buying a pool that only barely meets the retention target.

Surveillance NAS sizing checklist

Use this checklist before selecting hardware:

• [ ] Count every camera stream that will be recorded.
• [ ] Record the average bitrate in Mbps for each camera profile.
• [ ] Add audio and any separately recorded streams.
• [ ] Decide whether recording is continuous, scheduled, or motion-triggered.
• [ ] Convert the schedule into a recording factor from 0 to 1.
• [ ] Set the required retention in days or hours.
• [ ] Calculate camera storage with Cameras × Mbps × 10.8 × Days ÷ 1,000 for 24/7 decimal TB.
• [ ] Apply the recording factor when recording is not continuous.
• [ ] Add a documented allowance for filesystem, application, snapshot, and free-space needs.
• [ ] Convert the result to required usable post-RAID capacity.
• [ ] Select a RAID or ZFS layout based on redundancy and expansion requirements.
• [ ] Calculate aggregate network bandwidth and byte-rate workload.
• [ ] Check camera, codec, protocol, and surveillance-application compatibility.
• [ ] Confirm the NAS can handle concurrent recording, playback, indexing, and other services.
• [ ] Plan UPS protection and power for the NAS, drives, and PoE infrastructure.
• [ ] Decide whether the NAS, NVR, or both will manage recording.
• [ ] Create a separate backup or footage-export plan.
• [ ] Leave room for more cameras, higher bitrates, longer retention, and rebuild operations.

The most reliable estimate starts with real average bitrate measurements and ends with a capacity figure based on usable RAID-protected space—not raw disk labels. For systems that will also serve files, media, or backups, compare appropriate hardware in the NAS and storage servers category rather than sizing only for the camera streams.