Estimate CCTV recording capacity from camera count and average bitrate. Enter your recording schedule and retention target below, or use your usable drive space to estimate how many days it can hold. Results use decimal GB and TB.
Calculate recording storage
Calculations run in your browser. All cameras are assumed to use the entered average bitrate and recording hours. No headroom, audio allowance, RAID loss or file-system overhead is added automatically.
The CCTV storage formula
For a group of cameras with the same average recorded bitrate and schedule:
Recording GB = cameras × bitrate (Mbps) × hours/day × days × 0.45
Required GB = Recording GB × (1 + headroom percent / 100)
Required TB = Required GB / 1,000The factor 0.45 comes from unit conversion: 1 Mbps is 1,000,000 bits per second; multiply by 3,600 seconds per hour, divide by 8 bits per byte, then divide by 1,000,000,000 bytes per GB. That gives 0.45 GB per Mbps per recording hour.
For the basic check, 1 camera × 1 Mbps × 24 hours × 1 day × 0.45 = 10.8 GB, or 0.0108 TB, before any headroom. The display rounds numbers for readability; calculations keep their unrounded values. Very small positive results are shown with a “less than” sign instead of being presented as zero.
To estimate retention from usable storage:
Days = usable GB / [cameras × Mbps × hours/day × 0.45 × (1 + headroom / 100)]The target-days input affects required capacity only; the reverse calculation finds its own number of days. With zero recording hours, capacity is zero and a retention period is undefined, because no new footage is being written.
Choose the right average bitrate
Use the recorded stream’s measured or expected average bitrate, not its resolution alone. Two 4 MP cameras can use different storage because their encoding settings, frame rate, scene detail, noise, motion and average bitrate differ.
Check the camera or recorder’s encoding settings. If the setting is in kbps, divide by 1,000 to enter Mbps: 2,048 kbps = 2.048 Mbps. Mbps means megabits per second; a value in MB/s is megabytes per second and must be multiplied by 8 to become Mbps.
For constant-bitrate recording, the configured bitrate can be a starting estimate. For variable bitrate, a configured maximum is a ceiling rather than an observed average. Use representative recordings that include busy periods and day/night changes, or measure file size over a known duration. A quiet daytime scene may understate a noisy night scene.
Cameras with different settings
The main calculator assumes the same average bitrate and schedule for all entered cameras. If cameras share the same recording hours, you can use a weighted average bitrate. For four cameras at 2 Mbps and two at 4 Mbps, the average is (4 × 2 + 2 × 4) / 6 = 2.667 Mbps approximately.
For groups with different schedules, calculate each group separately and add their unrounded GB estimates. Include audio in the total recorded bitrate where it is part of the stream; account for separately recorded audio or other data separately if your bitrate measurement excludes it.
Recording hours, motion and headroom
Use 24 hours/day for continuous recording. For a fixed 12-hour recording schedule, use 12. For motion/event recording, enter the estimated actual recorded time, including pre-event and post-event clips, rather than the number of hours motion detection is enabled.
For example, a system armed all day that writes clips for an average of six hours uses 6 hours/day in this model. That average is an assumption, not a guarantee: rain, moving trees, traffic and false events can increase the amount recorded.
Headroom adds a planning margin to the recording estimate. With 10% headroom, 1,000 GB of estimated footage becomes 1,100 GB of planned capacity. The calculator starts at 0%, so it does not hide an extra allowance in the result. The appropriate margin depends on how uncertain your average bitrate and recording duration are.
For reverse estimates, the same margin increases the assumed space used per day and reduces the displayed retention. This margin does not calculate RAID parity, hot spares or reserved disk space for you.
Worked storage examples
All examples below use decimal units and 0% headroom. These are arithmetic examples using the stated bitrates, not claims about what a specific resolution or camera will consume.
| Camera setup | Schedule and retention | Recording capacity |
|---|---|---|
| 1 camera at 1 Mbps | 24 hours/day for 1 day | 10.8 GB = 0.0108 TB |
| 4 cameras at 4 Mbps each | 24 hours/day for 30 days | 5,184 GB = 5.184 TB |
| 8 cameras at 2 Mbps each | 12 hours/day for 30 days | 2,592 GB = 2.592 TB |
| 16 cameras at 4 Mbps each | 24 hours/day for 30 days | 20,736 GB = 20.736 TB |
For the four-camera example, 6 TB of usable recording space holds approximately 34.72 days before headroom: 6,000 / 172.8. If you add 10% planning headroom, the 30-day capacity target becomes 5,702.4 GB and the reverse estimate becomes approximately 31.57 days.
GB, TB and usable drive space
This tool uses decimal units: 1 GB = 1 billion bytes, and 1 TB = 1,000 GB. Operating systems and recorders may display capacity using binary units or different labels. GiB and TiB are different units; do not compare the numbers as if they were interchangeable.
For a reverse estimate, enter the capacity actually available for recording. Advertised drive capacity can differ from usable array capacity after RAID, spares, file-system use, system partitions and other files. For example, the sum of all installed drive labels is not necessarily the usable space in a RAID array.
The result is a planning estimate. Check the recorder’s actual retention after representative operation and adjust the bitrate, recording hours or margin. This calculator does not select a supported hard drive, determine an NVR’s maximum disk size or guarantee retention under every scene condition.
Frequently asked questions
How much space does one camera use per day?
At 24-hour recording with no added headroom, multiply the camera’s average Mbps by 10.8 GB/day. A 2 Mbps camera uses an estimated 21.6 GB/day; a 4 Mbps camera uses 43.2 GB/day. Use the actual average bitrate, not a resolution preset.
How many days can a 1 TB drive record?
It depends on the total recorded bitrate, hours and usable space. At 1 camera, 1 Mbps, 24 hours/day and no headroom, 1,000 GB holds about 92.59 days. At 4 cameras and 4 Mbps each, the same usable capacity holds about 5.79 days.
Does H.265 always use half the space of H.264?
No fixed ratio is applied here. If H.265 reduces the actual average recorded bitrate in your installation, enter that lower measured value. A codec label alone is not a capacity figure, and two streams at the same Mbps consume the same estimated bytes over the same duration in this model.
Can I use this for an NVR, DVR or SD card?
The bitrate calculation can estimate recorded video size for any of them, provided the entered bitrate, recorded hours and usable space describe the actual recording. Check the device’s own storage support and overhead separately.
Why does my recorder keep fewer days than the estimate?
Recheck VBR averages over busy and night scenes, actual motion-clip time, multiple recorded streams, audio, usable capacity and overwrite settings. An incomplete average or an optimistic event duration can substantially understate storage use.
Related camera guides
- ONVIF Device Manager: inspect compatible cameras and media profiles.
- RTSP and ONVIF ports: understand device services and video-stream connections.
- Dahua ConfigTool: find and configure supported Dahua devices.
- DMSS / SmartPSS Lite on a computer: live viewing and playback after setup.
- Wisenet Viewer: view compatible recorders and export recorded clips.