Surveillance Retention Time Calculator
What the Surveillance Retention Time Calculator does
The Surveillance Retention Time Calculator estimates how many days of security camera footage can fit on your available storage. It combines your total storage capacity, an estimated usable storage percentage, the number of cameras, their average recording bitrate, and the number of hours each camera records per day.
The result, labeled Estimated Retention, is shown in days. For example, an estimate of 41.67 days means the specified storage could hold approximately 41 days and 16 hours of footage under the entered conditions. On a system configured to overwrite old recordings when storage fills, that is approximately how far back you could expect footage to remain available.
This is a planning estimate, not a guarantee. Actual retention can change as scene activity, compression, recording schedules, and storage overhead change. The calculation also assumes that all cameras use the same average recorded bitrate and recording schedule.
How to use the Surveillance Retention Time Calculator
Gather the storage and recording details for your surveillance system, then enter the following values:
- Total storage capacity (TB, decimal): Enter the total capacity available for the recordings in decimal terabytes. The calculator uses 1 TB as 1,000,000,000,000 bytes. For example, enter 8 for an 8 TB storage capacity.
- Estimated usable storage: Choose 90%, 80%, or 100% usable. This factor accounts for capacity reserved for formatting and system overhead. The illustrative default is 90%; use the option that best reflects your system.
- Number of cameras: Enter the number of cameras whose footage will use that storage. The calculator treats every camera as having the same bitrate and daily recording time.
- Average recording bitrate per camera (Mbps): Enter the average bitrate of the footage actually recorded by each camera, in megabits per second. Include audio or additional streams if they are stored as part of that camera’s recording.
- Recording hours per day per camera: Enter the average number of hours each camera records every day. Use 24 for continuous recording or a lower average for a shorter schedule.
Read the Estimated Retention result in days. You can change the inputs to compare scenarios, such as adding cameras, increasing storage, or recording fewer hours per day. Keep the assumptions consistent when comparing results.
How the Surveillance Retention Time Calculator formula works
The calculation divides usable storage by the amount of video data recorded per day. It converts decimal terabytes into megabits so storage capacity and bitrate use compatible units:
Estimated retention in days = (storage capacity in TB × usable storage factor × 8,000,000) ÷ (number of cameras × bitrate in Mbps × recording hours per day × 3,600)
One decimal terabyte contains 8,000,000 megabits, and one hour contains 3,600 seconds. The denominator estimates the combined data recorded by all cameras each day. A larger usable capacity increases estimated retention; more cameras, a higher average bitrate, or longer daily recording time reduces it.
Worked example: four cameras and 8 TB of storage
Suppose you use the calculator’s illustrative default values: 8 TB of total storage, 90% usable storage, four cameras, an average recorded bitrate of 4 Mbps per camera, and 24 hours of recording per camera each day.
- Usable storage: 8 TB × 0.90 = 7.2 TB.
- Usable storage in megabits: 7.2 × 8,000,000 = 57,600,000 megabits.
- Data recorded per day: 4 cameras × 4 Mbps × 24 hours × 3,600 seconds = 1,382,400 megabits.
- Estimated Retention: 57,600,000 ÷ 1,382,400 = 41.67 days, rounded to two decimal places.
The 90% usable factor and 4 Mbps bitrate in this example are assumptions for illustration. Your system may have different usable capacity and recorded bitrates, so replace them with values that reflect your setup.
Use cases for the Surveillance Retention Time Calculator
Planning a new camera system. Before choosing storage for a network video recorder or another recording system, estimate how long the planned camera count and recording settings could retain footage. Run several storage capacities to see how the estimate changes.
Adding cameras to an existing system. More cameras typically produce more recorded data. If the new cameras have similar recording settings, enter the new total camera count to estimate the effect on retention. If they use different bitrates or schedules, the calculator’s equal-camera assumption makes the result less precise.
Comparing continuous and scheduled recording. Recording 24 hours a day uses more storage than recording for a shorter period at the same average bitrate. For instance, an illustrative setup with 4 TB of storage, 80% usable capacity, eight cameras, 2 Mbps per camera, and 12 recording hours per day produces an estimate of 37.04 days. The result depends on those assumed values.
Checking a retention goal. If you want to keep footage for a certain number of days, compare that goal with the estimate. Leave room for variation and check the system’s actual recording history before relying on the projected period.
Other factors to consider when calculating Estimated Retention
Variable bitrate and scene activity: Some cameras use variable bitrate recording, so storage use rises or falls with the amount of movement and detail in a scene. A busy entrance may use more data than a quiet room at the same configured settings. An average measured over a representative period is more useful than assuming the bitrate stays constant.
Resolution, frame rate, and compression: These settings can affect the recorded bitrate. Higher resolution or frame rate may increase storage use, while compression settings can change how much data is needed. Use the resulting average recorded bitrate in Mbps rather than relying on resolution alone.
Recording schedules and gaps: Continuous, scheduled, and motion-triggered recording can produce different amounts of footage. For intermittent recording, enter an estimated average number of recording hours per day. Changes in motion activity, missed recordings, or system downtime can make the actual total differ from that average.
Usable capacity and other files: Formatting and system overhead reduce the space available for footage. The usable-storage selection is an estimate, and the calculator does not separately subtract space used by other files. If other data shares the storage, account for it when choosing the capacity and usable factor.
Different camera settings: Cameras may record at different bitrates or for different lengths of time. This calculator applies one bitrate and one schedule to every camera, so its estimate is most representative when the cameras have similar settings.
Storage behavior: Retention also depends on how your recorder manages a full drive. Some systems overwrite the oldest footage, while others may have different settings. Check the recorder’s configuration and actual footage history to confirm how long recordings remain accessible.
Surveillance Retention Time Calculator FAQ
What does the Estimated Retention result mean?
It is the approximate number of days that the entered usable storage can hold the calculated recording volume. It assumes the same average bitrate and recording hours for every camera. Actual retention may be shorter or longer as recording conditions change.
Should I choose 80%, 90%, or 100% usable storage?
Choose the percentage that best represents the space available after formatting and system overhead. The calculator’s illustrative default is 90%. Select 80% if that better reflects your system, or 100% only when you are estimating with all entered capacity available for the recordings.
How does adding another camera affect retention?
With storage, bitrate, and recording hours unchanged, adding a camera increases the total data recorded each day and reduces estimated retention. The calculation assumes the added camera records at the same average bitrate and for the same number of hours as the others.
Can I use the calculator for motion-triggered recording?
Yes. Enter your estimated average recording hours per day per camera and an average bitrate that reflects the footage stored during those hours. Treat the result cautiously because motion activity and recording duration can vary considerably from day to day.
Does a 4 Mbps camera always use the same amount of storage?
Not necessarily. A 4 Mbps value can be an average, while actual data rates may vary with motion, scene detail, compression, and recording settings. Audio and additional stored streams also consume space, so include them when estimating the average recorded bitrate.