How Much Storage Do Security Cameras Need?

The storage a security camera needs comes down to three numbers: its bitrate, how many hours a day it records, and how many days of footage you want to keep. As a rough rule, a 1080p camera recording nonstop around 2 Mbps uses about 21.6 GB per day, while the same camera recording only on motion for three hours uses closer to 2.7 GB. This guide shows the arithmetic, gives sample sizes for microSD cards and network video recorders, and explains how to leave a sensible safety margin.

The one formula worth remembering

Video size is bitrate multiplied by time. Cameras describe bitrate in megabits per second (Mbps), while storage is sold in gigabytes (GB). Since eight bits make a byte, and a day has 86,400 seconds, the conversion simplifies neatly:

Storage per day in GB is roughly the bitrate in Mbps multiplied by 10.8, if the camera records all day.

For partial recording, scale it down. A camera at 2 Mbps records about 0.9 GB per hour (2 x 0.45). If it records for three hours a day, that is 2.7 GB. Multiply by the number of days of history you want, and you have the base requirement before any safety margin.

Where to find your camera’s bitrate

Many cameras let you choose a quality or bitrate setting in the app or web interface, and manuals or spec sheets often list a typical range. Wired and network cameras usually expose a clear number, while some consumer wireless cameras hide it behind quality presets. If you cannot find the figure, use the typical values below as a starting estimate and check the actual size of a few saved clips to calibrate.

Bitrate varies with the scene. A camera watching an empty hallway can compress very well, while busy traffic, rain, snow, insects and low-light noise make the file larger. Cameras set to variable bitrate will fluctuate, while constant bitrate cameras stay near a set value. Newer compression formats such as H.265 commonly reduce file size noticeably compared with H.264 at similar quality, though support depends on the camera and recorder.

Typical sizes by resolution

These bitrates are assumptions chosen for easy arithmetic and are common ballpark figures, not guarantees for any model. Your camera could sit well below or above them. Use the table to see the scale of the problem: nonstop recording at higher resolutions is far larger than most people expect.

Continuous recording versus motion recording

Continuous recording captures everything, which is helpful if you want to scrub back to an exact moment, and it removes any chance that a motion sensor misses an event. The cost is storage. Motion or event recording saves only clips triggered by movement, people, vehicles or packages, and it typically uses a small fraction of the space.

Many people choose a hybrid: motion recording during the day and continuous recording overnight, or continuous recording only for a front door. If a camera is placed where little happens, motion recording keeps clips short and easy to review. Some systems also record a few seconds before the trigger, called pre-roll, which uses slightly more space but catches the start of the event.

Worked example: microSD cards

Many cameras record to a microSD card inside the unit. Suppose a 1080p camera averages 2 Mbps and the card is a nominal 128 GB. Card capacity is quoted in decimal gigabytes, and a small part is used by formatting and file management, so assume around 120 GB usable.

• Continuous recording: 120 / 21.6 is about 5.5 days of history before the card starts overwriting the oldest footage.
• Motion recording, three hours a day: 120 / 2.7 is about 44 days.
• A nominal 256 GB card: roughly double these figures, so about 11 days continuous or 88 days of motion clips, using the same assumptions.

Check the maximum card size listed in the camera’s manual, because supported capacity varies. Use cards marketed for continuous recording or high endurance, since ordinary cards can wear out when overwritten constantly. Remember that a card inside the camera can be taken along with it, so keep important clips backed up if the camera is easy to reach.

Worked example: a four-camera recorder

A network video recorder (NVR) or digital video recorder stores footage on an internal hard drive. Assume four 4 MP cameras at 4 Mbps each, recording continuously. Total bitrate is 16 Mbps.

• Daily storage: 16 x 10.8 = 172.8 GB.
• 14 days of history: 172.8 x 14 is about 2.4 TB.
• 30 days of history: 172.8 x 30 is about 5.2 TB.

Add a margin of 10 to 20 percent for bitrate spikes, audio and drive formatting. In practice, that means a 4 TB drive for two weeks or a 6 TB to 8 TB drive for a month. Drives designed for around-the-clock surveillance use are commonly recommended over ordinary desktop drives, and the recorder’s manual will state the largest drive it supports.

Cloud storage and hybrid setups

Cloud storage moves the capacity problem to the provider. Most services keep a limited window, such as a few days or weeks, and charge a recurring plan, so the question changes from how many gigabytes to how long the plan retains clips. Some systems pair a local card or recorder with the cloud, which gives a backup if the camera is removed or loses internet. When comparing, check how long clips are kept, whether continuous recording is supported and whether exporting clips is easy.

Common sizing mistakes

• Mixing up megabits and megabytes. A lowercase b means bits and an uppercase B means bytes, so a 2 Mbps stream is only 0.25 MB per second.
• Ignoring night footage. Low-light video is noisier and often produces larger files than daylight video.
• Counting the label capacity as usable. Formatting, file systems and the way vendors count gigabytes reduce the real space a little.
• Forgetting extra streams. Some cameras record a main stream and a lower-quality sub-stream, and audio adds a small amount more.
• Assuming motion recording always means small files. A camera pointed at a tree or road may trigger constantly and behave almost like continuous recording.

Checklist for sizing your storage

1. List each camera and its resolution and bitrate (or assume the table values).
2. Decide on continuous, motion or hybrid recording, and estimate recording hours per day.
3. Choose the number of days of footage you actually need. Two weeks suits many homes.
4. Multiply: bitrate x 0.45 x hours per day x days, in GB.
5. Add a 10 to 20 percent margin and round up to the next common size.
6. Confirm the maximum card or drive size your equipment supports.
7. Save important clips elsewhere, because loop recording overwrites old footage automatically.

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Frequently asked questions

How much storage does one security camera need per day?

It depends on bitrate and recording time, so there is no single answer. At 2 Mbps, a camera recording nonstop uses about 21.6 GB per day, while three hours of motion clips use around 2.7 GB. Multiply the bitrate in Mbps by 10.8 for a nonstop day, then adjust for the hours actually recorded.

What size microSD card should a security camera use?

Choose a size the camera’s manual says it supports, within reason, and prefer cards sold for continuous recording or high endurance. For motion recording at 1080p, 128 GB often gives several weeks of history under typical assumptions. Continuous recording at the same quality fills a card of that size within about a week, so plan accordingly.

How many terabytes does an NVR need for four cameras?

Four 4 MP cameras at an assumed 4 Mbps each recording nonstop use about 173 GB daily. That is roughly 2.4 TB for two weeks or 5.2 TB for a month, before a safety margin. Adding 10 to 20 percent and rounding up suggests 4 TB or 6 TB to 8 TB drives.

Does H.265 really save space compared with H.264?

Commonly, yes. The newer H.265 format can often reduce file sizes noticeably at similar visual quality, which helps with long retention, with savings often described as up to around half in favorable conditions. The benefit depends on the camera, scene and settings, and both camera and recorder must support it, so check the specifications.

What happens when the storage fills up?

Most cameras and recorders use loop recording, which overwrites the oldest footage once the card or drive is full. Some can be set to stop instead, and many send a warning when space runs low. Export and save important clips before they are overwritten, and check the settings so you know which behavior your equipment uses.