How to calculate storage for an IP camera NVR

Choosing an NVR based solely on the number of cameras is insufficient. Two installations with eight cameras might require vastly different disk capacities: one records 24/7 at high resolution, while the other only saves motion events. Storage depends on actual bitrate, recording hours, retention days, codec, and the number of cameras.

Calculating this before purchasing prevents two problems: losing recordings before the planned retention period or paying for capacity that is never used. It also allows you to check if the recorder supports the necessary number and size of disks.

The five data points you need

1. Number of cameras that will record simultaneously.
2. Average bitrate of each camera in megabits per second.
3. Hours recorded per day.
4. Days you want to retain recordings.
5. Margin for peaks, audio, metadata, and future changes.

Resolution and frames per second influence storage, but the actual data occupying disk space is the bitrate. Two 4K cameras can use different amounts if one operates at 15 fps with efficient compression and another at 30 fps in a scene with a lot of movement.

Practical formula

For a simple estimate:

GB per day ≈ bitrate in Mb/s × 10.8

This result corresponds to one camera recording 24 hours. Then multiply by cameras and days. For example, four cameras at 4 Mb/s consume approximately 43.2 GB daily each: about 172.8 GB per day and 2.42 TB in 14 days. Add a 15% to 25% margin.

These are examples, not exact promises. Measure or configure the actual bitrate of your camera model and scene.

Continuous or event-based recording

Continuous recording is easy to size and preserves context before and after any incident. It consumes more space. Motion-based recording can significantly reduce occupancy in quiet areas, but it depends on well-tuned detection. Rain, vegetation, shadows, or traffic can trigger almost constant events.

A balanced strategy involves continuous recording at a moderate stream and using events to mark relevant moments, or defining different schedules per camera. In a store, access points and cash registers might require continuity, while a closed warehouse could use event-based recording outside business hours.

H.264, H.265, and scene reality

H.265 typically reduces bitrate compared to H.264 for comparable quality, especially at high resolutions. However, savings depend on the camera, firmware, motion, night noise, and configuration. Night vision with grain can occupy more space than a static daytime scene.

You should not size a critical installation using only the best advertised percentage. Configure a representative camera, record for several days, and check the average bitrate and peaks. This test also detects if the NVR's input bandwidth is sufficient.

Choosing eight or sixteen channels

The number of channels indicates how many cameras the NVR can manage, but also check maximum resolution, incoming bandwidth, codec, number of bays, and maximum capacity per disk. For an installation of up to eight cameras with limited growth, an Ajax 8-channel NVR with space for one HDD up to 16 TB might fit if the calculation fits within that bay.

If you already have nine cameras planned, or the layout includes new areas, starting with an Ajax 16-channel 4K NVR with H.265/H.264 avoids replacing the recorder too soon. Always confirm disk capacity and bandwidth for the specific variant.

The security recorder collection allows comparing NVRs and DVRs. NVRs are oriented towards IP cameras; DVR/XVRs typically handle coaxial cameras or hybrid systems depending on the model.

Full example for a store

Imagine six cameras: four indoor at 3 Mb/s and two outdoor at 5 Mb/s. The total is 22 Mb/s. Recording 24 hours, the approximate daily consumption is 22 × 10.8 = 237.6 GB. For 30 days, 7.13 TB. With a 20% margin, plan for about 8.56 TB of usable space.

A nominal 10 TB disk might fit, but the space shown by the system will be less due to the difference between decimal and binary units, as well as management space. If you expect to add two cameras, recalculate now: reserving channels without reserving storage only postpones the problem.

Don't forget the right disk

Use disks designed for video surveillance and continuous operation when the system records 24/7. A desktop disk may not be optimized for sustained writes, vibration, and multiple streams. Check NVR compatibility and do not exceed the maximum capacity per bay.

The disk alone is not a backup. If images are critical, define incident export, physical protection of the recorder, users with permissions, and, when appropriate, redundancy. RAID improves availability against disk failure, but it does not protect against deletion, theft, or fire.

Pre-purchase Checklist

• Current and planned channels for two years.
• Resolution, fps, and bitrate per camera.
• Continuous, event-based, or mixed schedule recording.
• Truly necessary retention days.
• Audio and analytics that add data.
• Bays, maximum capacity, and compatible disks.
• NVR input bandwidth.
• Video output and remote access.
• 15–25% margin.
• Policy for exporting and accessing evidence.

Common mistakes

Calculating by megapixels without bitrate. Compression and the scene change consumption.

Assuming motion equals a fixed 10%. Measure actual activity; a street can record all day.

Filling all channels without network margin. The NVR may support cameras, but not their aggregated bitrate.

Confusing nominal TB with usable space. Reserve capacity for differences and system overhead.

Reducing the bitrate so much that details are no longer recognizable. Validate quality for faces, license plates, or areas of interest before finalizing the calculation.

Frequently Asked Questions

How much space does a 4 Mb/s camera occupy per day?

Approximately 43.2 GB if it records 24 hours, before margin and variations.

Does H.265 always occupy half the space of H.264?

No. It can save a lot, but the result depends on the scene, configuration, and hardware.

Is it better to record by motion?

It reduces space in quiet areas, but it needs well-tuned detection. For critical areas, consider continuous recording or a mixed mode.

Can I put any hard drive in an NVR?

It must be compatible in interface and capacity. For continuous recording, specific video surveillance disks are recommended.

How many days should I retain recordings?

It depends on the risk, operation, and applicable requirements. Define when incidents are usually detected and consult the data protection obligations for your case.