"How many days of footage will I have?" is one of the first questions we get on camera quotes, and it deserves a real answer, not a shrug. The math is not complicated. It is just rarely explained.
Here it is in plain terms.
The four numbers that matter
Retention comes down to four things:
- How many cameras are recording.
- Bitrate per camera, which is driven by resolution, frame rate, and how much motion the scene contains.
- Recording mode: continuous, motion-only, or a mix.
- How much disk the recorder has.
Everything else, brand included, is detail. A camera producing video at a given bitrate fills disk at a fixed rate, and the recorder keeps footage until the disk is full, then overwrites the oldest material.
A worked example, in round numbers
Take a typical modern 4K camera recording continuously at a moderate bitrate. In rough terms it writes something like 40 to 90 GB per day depending on settings and how busy the scene is. Call it 60 GB per day as a middle figure.
Now a common setup: six of those cameras and an 8 TB drive in the recorder.
Six cameras at roughly 60 GB each is about 360 GB per day. Eight terabytes is about 8,000 GB. Divide, and you get a little over three weeks of continuous footage before the oldest video starts being overwritten.
Swap those 4K cameras for 2K models and the per-camera figure roughly halves, so retention roughly doubles. Drop the frame rate from 30 to 15 and you claw back more still, usually with no practical loss for security purposes. Nobody reviews a break-in frame by frame at 30 fps.
The point is not the exact figures, which vary by scene and compression. The point is that retention scales in straightforward ways: double the disk, double the days; double the cameras or the bitrate, halve them.
The motion-only temptation
Motion-only recording is the setting that makes small drives look adequate. If cameras only record when something moves, a quiet property might multiply its retention several times over. Tempting.
We generally advise against relying on it, for one reason: evidence.
Motion detection has to decide, in the moment, what counts as an event. It misses things. A person moving slowly at the edge of frame, activity in rain or snow, a subject partially hidden by a parked car. Insurance adjusters and police do not just want the dramatic ten seconds; they want the hour before, the vehicle that drove past twice, the moment someone first entered frame. With motion-only recording, the gaps are precisely where the questions end up.
Continuous recording has no opinion about what matters. It is all there. When something serious happens, that completeness is worth far more than the extra weeks of retention motion-only would have bought you.
A sensible compromise many recorders support: record continuously at a modest quality, and flag motion events on top for quick searching. You keep the full timeline and the fast navigation.
How much retention do you actually need
For most homes, two to four weeks of continuous footage is a comfortable target. Incidents are usually discovered within days. The awkward cases, a cottage checked monthly or damage noticed after a vacation, argue for a month or more, and we sized camera counts themselves in how many cameras a house actually needs if you are still at that stage.
Small businesses often want 30 to 90 days, and some situations (certain workplaces, licensed premises) have retention expectations set by insurers or regulators, so check before buying the drive.
Two practical notes on the disk itself. Buy surveillance-rated drives, which are built for constant writing, not desktop drives. And buy bigger than the math says you need, because you will add a camera later. Everyone does. Going from a 4 TB to an 8 TB drive at purchase time typically costs $100 to $200 more and doubles your margin for error.
Do the math before you buy
Sketch it on paper: cameras, times daily gigabytes, into total disk. Five minutes of arithmetic prevents the common disappointment of discovering, after an incident, that the recorder only held six days.
When we design and install camera systems we run these numbers for every quote, sized to how you will actually use the footage. If you would like retention that is planned rather than discovered, our security camera installation service is the place to start.
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