How Many Days Does a Security Camera Record? Working Out Disk Size

What decides how long a security camera records?

The recorder (an NVR or DVR) writes the camera footage to disk continuously. When the disk is full, it deletes the oldest footage and keeps writing over it. So the answer to “how many days does it keep” depends on how quickly the disk fills each day, and that is decided by four things:

• Bitrate: the amount of data a camera produces per second, in Mbps. This is the figure at the centre of the calculation.
• Camera count: every camera adds its own bitrate to the disk.
• Recording mode: continuous, or only when motion is detected.
• The scene itself: trees moving in the wind, passing traffic and night-time grain all produce far more data than an empty corridor.

Resolution is not on that list on its own, because resolution affects the disk only through bitrate. The same 4 MP camera can write 20 GB a day or 60 GB a day depending on how it is configured.

How do you work out daily storage?

A bitrate of 1 Mbps is 125 kilobytes per second. With 86,400 seconds in a day, one megabit per second of continuous recording uses about 10.8 GB a day. The whole calculation follows from that figure:

• Daily storage (GB) = combined camera bitrate (Mbps) × 10.8
• Retention (days) = disk capacity (GB) ÷ daily storage (GB)

For example, four 4 MP cameras running at 2.5 Mbps on H.265 produce 10 Mbps between them. That is about 108 GB a day. A 2 TB disk holds about 18 days on this system, and a 4 TB disk about 37 days.

There is no need to guess the bitrate: it is shown on the video settings screen of the recorder or the camera. If the setting is “variable bitrate” (VBR), the figure shown is a ceiling and the real average usually sits below it, which keeps the calculation on the safe side.

How many days do 1 TB, 2 TB and 4 TB disks hold?

The figures below assume H.265, 15 frames per second and continuous recording. Real retention varies with the scene, so treat them as a starting point.

• Four 2 MP cameras (about 1.5 Mbps each, 65 GB a day): about 15 days on 1 TB, about 31 days on 2 TB.
• Four 4 MP cameras (about 2.5 Mbps each, 108 GB a day): about 9 days on 1 TB, 18 days on 2 TB, 37 days on 4 TB.
• Eight 4 MP cameras (about 2.5 Mbps each, 216 GB a day): about 9 days on 2 TB, 18 days on 4 TB, 37 days on 8 TB.
• Four 8 MP (4K) cameras (about 5 Mbps each, 216 GB a day): about 9 days on 2 TB, 18 days on 4 TB.

If the same cameras run H.264, roughly halve these figures. They are for continuous recording; motion recording extends them, but by how much depends entirely on the scene.

How much longer does motion recording keep footage?

With motion recording, the recorder only writes to disk when something moves in the scene. For a store room that sits empty overnight, an office closed at the weekend or a back garden nobody walks through, that can multiply retention several times over. At a shop entrance with people and traffic passing all day, it gains almost nothing. In most homes and businesses with mixed activity, expecting roughly one and a half times the continuous figure is realistic.

It has a cost. Set the sensitivity wrong and either the first seconds of an incident are missed, or a branch moving in the wind, rain and passing headlights keep recording running almost non-stop. That is why combining the two usually works best: critical points such as entrances and tills record continuously, and quiet areas record on motion. With the pre-record buffer switched on, the few seconds before motion starts are captured as well.

Why does night footage take more space?

In the dark, a camera amplifies the image electronically, and that adds grain. The codec records that grain as detail that keeps changing, so the bitrate rises even when the scene is completely empty. A camera running on variable bitrate can produce noticeably more data at night than during the day.

The practical consequence: measure the bitrate in daylight, base the calculation on it, and real retention will come out shorter than you worked out. Check the numbers against at least one night-time measurement. Adding lighting where the infrared falls short both sharpens the picture and reduces disk use.

How can retention be extended without losing quality?

Before buying a larger disk, there are settings worth trying that cost the picture almost nothing:

• Switch to H.265: if the cameras and recorder support it, this is the biggest single gain.
• Lower the frame rate: 12–15 frames per second is enough for security recording in most cases, and dropping from 25 to 12 cuts disk use noticeably.
• Enable a smart codec mode: modes such as H.265+, which avoid recording the unchanging parts of a scene again and again, save a great deal on quiet scenes.
• Do not give every camera the same settings: an entrance camera that needs to capture faces and number plates stays at a high bitrate, while a garden camera watching a wide area can be turned down.
• Move cameras that rarely see movement to motion recording.

If retention is still too short after that, capacity has to increase. Recorders with more than one drive bay can take an extra disk without deleting existing footage; single-bay recorders need a move to a larger disk. We cover installation and configuration on the security camera systems page.

Which disk should a CCTV recorder use?

The disk in a recorder writes 24 hours a day. Disks made for desktop computers are not designed for that load; they fail early, and when they fail they take part of the footage with them. A recorder should use surveillance-class disks designed for continuous writing, such as the WD Purple or Seagate SkyHawk ranges.

Checking disk health in the recorder’s interface from time to time is the easiest way to catch a failure before footage is lost. Many recorders can also send a phone notification when a disk fails, which requires the recorder to be set up for remote viewing. We explain how to set up phone access in viewing security cameras on your phone, and periodic checks on the security system maintenance and repair page.

How many days is enough, and what does data protection law say?

The right target depends on how long it takes you to notice an incident. In a shop that opens and closes every day, problems usually surface within a few days; at a holiday home, a store room or a property you rarely visit, weeks can pass. Fifteen days is a practical target for most homes, and thirty for most businesses.

Longer is not always better. Türkiye’s data protection law (KVKK) does not set a fixed number of days for camera footage, but it does require personal data to be kept only for as long as the purpose it was collected for requires. Footage kept far longer than any security purpose needs is a liability rather than an asset. Some sectors may have minimum retention periods set by regulation or by provincial decisions; where such a requirement applies, it takes precedence.

Once you have a target, setting the recorder to it and letting it overwrite the oldest footage when the disk fills keeps that balance automatically. We cover the other data protection duties in our security systems guide.