Security cameras · motion
Motion event storage calculator.
Estimate the disk used when cameras record only on motion, and compare it with continuous recording.
Inputs
Motion storage
Enter the numbers above.
How much storage does motion recording use?
With motion recording, the camera writes only while something is happening. Each event records for its own length plus a pre-event and post-event buffer. Multiply the events per day by that total time to get the seconds recorded, then by the bitrate. An optional idle stream models a cheap low-bitrate recording kept between events. The tool caps recorded time at 24 hours a day.
Worked example. Each camera sees 60 events a day averaging 20 s with a 10 s buffer, so it records 60 x 30 s = 30 minutes, or 2.1 percent of the day. At 4 Mbps that is 0.9 GB per camera per day, 3.6 GB per day for four cameras, and 0.108 TB over 30 days. Continuous recording at 4 Mbps for the same cameras would need 5.18 TB.
The number of events is the uncertain part. Wind, trees, insects and headlights can multiply it, so measure for a week on your own site and adjust the estimate.
Frequently asked questions
How much storage does motion detection save compared with continuous?
In the default example four cameras use 0.108 TB over 30 days instead of 5.18 TB, because they record about 2 percent of the day. Your savings depend on how often motion triggers.
Why add a pre and post buffer?
Recorders keep a few seconds before and after each trigger so the clip shows how the event started and ended. Those seconds add to the storage.
What if motion triggers constantly?
Then the recorded time approaches the whole day and the tool caps it at 24 hours, matching continuous recording.
How do I estimate events per day?
Count the clips your system saves over a week and divide by seven and by the number of cameras. Busy outdoor views can produce far more events than indoor ones.
Sources
Method
- Plain bitrate x time arithmetic (bits to bytes divide by 8; 86,400 seconds in a day). Event counts, lengths and buffers are your own estimates.
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Scope
Planning estimate only. Not a security design; check local recording and privacy rules. Event counts, lengths and buffers are your estimates; real numbers vary with the scene.