Quick answer
With the default example, 4 cameras at 2 Mbps for 24 h/day and 30 days need about 3.11 TB including headroom. A 4 TB drive gives about 38.6 days under the same assumptions.
How to use this security camera storage calculator
Start with the average recorded bitrate per camera. If your NVR or camera data sheet gives a bitrate in Mbps, use that number directly. If not, use the bitrate helper to estimate a starting point from resolution, codec, frame rate, and scene complexity.
Then enter how many hours per day the system records and how many days you want to keep footage. Continuous recording is usually 24 hours per day. Motion or event recording should use the realistic number of recorded hours per day, not the number of hours the camera is powered on.
If you are also powering IP cameras from a switch, use the PoE Switch Power Budget Calculator to check watts, port count, and per-port PoE standard before buying the switch.
Security camera storage formula
total bitrate Mbps = camera count x bitrate per camerastorage per day GB = total bitrate Mbps x recording hours x 3600 / 8 / 1000raw storage TB = storage per day GB x retention days / 1000recommended storage TB = raw storage TB x (1 + headroom %)The formula uses bitrate because video storage is driven by how much data the camera records per second. Resolution, codec, frame rate, and scene motion matter because they change bitrate, but bitrate is the number that directly drives storage.
Assumptions and methodology
This calculator estimates decimal TB for practical drive purchasing. It does not guarantee exact retention because real surveillance video often uses variable bitrate, and the NVR may add file system, database, audio, event, or metadata overhead.
- Use maximum or realistic average bitrate from the camera or NVR when available.
- Increase headroom for night scenes, rain, trees, traffic, infrared noise, and busy entrances.
- Use recording hours per day to model motion recording, but do not assume motion recording will always be quiet.
- For critical commercial retention policies, validate the design against the NVR vendor's storage behavior before purchase.
Example calculations
4-camera NVR storage example
Suppose four cameras record at 2 Mbps each, 24 hours per day, for 30 days. The total bitrate is 8 Mbps.
The raw video estimate is 2.59 TB. With 20% headroom, the recommended storage becomes 3.11 TB. That is why a 4 TB drive is a practical starting point for this example.
If you double the camera count, double the bitrate, or double the retention period, the storage requirement roughly doubles. Codec and motion recording can reduce storage, but they should be treated as assumptions, not guarantees.
NVR storage size chart
These examples use common planning values and include headroom. Replace the bitrate with your actual camera or NVR value when possible.
| Setup | Schedule | Retention | Per day | Recommended | Example drive | Result |
|---|---|---|---|---|---|---|
| 4 cameras @ 2 Mbps | 24 h/day | 30 days | 86 GB | 3.11 TB | 4 TB | Storage fits |
| 8 cameras @ 2 Mbps | 24 h/day | 30 days | 173 GB | 6.22 TB | 6 TB | More storage needed |
| 8 cameras @ 4 Mbps | 24 h/day | 30 days | 346 GB | 12.4 TB | 12 TB | More storage needed |
| 16 cameras @ 3 Mbps | 24 h/day | 30 days | 518 GB | 19.4 TB | 16 TB | More storage needed |
| 4 cameras @ 8 Mbps | 24 h/day | 30 days | 346 GB | 13 TB | 12 TB | More storage needed |
Why bitrate matters more than resolution
Resolution tells you how many pixels the camera can capture, but bitrate tells you how much data is actually written to storage. A busy 1080p camera at a high bitrate can use more storage than a quiet 4MP camera at a low bitrate. H.265 and smart encoding can reduce storage, but the real result depends on the encoder and the scene.
For the best estimate, check the NVR's live bitrate reading after the system has been running during both day and night. Use the higher realistic value if the retention target matters.
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FAQ
How do I calculate NVR storage for security cameras?
Multiply camera count by the average recorded bitrate, recording seconds per day, and retention days. Divide by 8 to convert bits to bytes, then convert to GB or TB. Add headroom for bitrate spikes, formatting, metadata, and future changes.
How much storage do I need for 4 security cameras?
It depends mostly on bitrate and retention. Four cameras at 2 Mbps each recording 24/7 for 30 days need about 2.6 TB before headroom and about 3.1 TB with 20% headroom.
How much storage do I need for 8 cameras for 30 days?
Eight cameras at 2 Mbps each recording continuously for 30 days need about 5.2 TB before headroom and about 6.2 TB with 20% headroom. Higher bitrate, 4K resolution, night noise, or busy scenes can increase this quickly.
Is bitrate more important than resolution for NVR storage?
Yes. Resolution influences bitrate, but storage is calculated from the actual recorded bitrate. A 4K camera at a low bitrate can use less storage than a 4MP camera at a high bitrate.
Does H.265 always cut storage in half?
No. H.265 often reduces storage compared with H.264, but actual savings depend on camera encoder quality, scene motion, night noise, GOP settings, and whether the NVR records the stream efficiently.
Should I calculate storage in TB or TiB?
Drive labels usually use decimal TB, while operating systems may display binary TiB. For buying drives, TB is practical, but keep headroom so the TB/TiB difference does not break the retention target.
Does motion recording reduce storage?
Usually yes, if the NVR truly records fewer hours per day. Use the recording-hours input to model motion or event recording, but leave extra headroom for busy days, weather, night noise, and false motion triggers.
Why does my real NVR storage differ from the calculator?
Real usage can differ because of variable bitrate, audio, metadata, pre-record buffers, substreams, camera firmware, NVR overhead, file system formatting, drive reporting, and scene complexity.