CCTV & Surveillance
CCTV Storage: How Much Hard Drive Space Do You Need?
How many days of footage a CCTV recorder keeps depends on cameras, bitrate and recording mode. Here is a simple formula, worked examples, and how to choose the drive.
The most common CCTV complaint after installation is not a bad picture. It is discovering, the day after an incident, that the footage has already been overwritten. How long a recorder keeps footage depends on a few numbers that are easy to work out before buying the hard drive.
This guide gives a simple formula, worked examples, and practical advice on choosing surveillance drives.
What decides how much storage you need
Four things determine how quickly a recorder fills its drive:
- Number of cameras
- Bitrate of each camera: how much data per second it records, which rises with resolution and scene activity
- Recording mode: continuous, or only when motion or an event is detected
- Compression: H.265 and smart codecs use much less space than older H.264
The bitrate is the key number. Recorders and cameras let you set it, and it appears in the recording settings.
The formula
Storage per day, in gigabytes, is roughly the bitrate in megabits per second multiplied by 10.8.
That comes from 86,400 seconds in a day, divided by 8 bits per byte, divided by 1,000 megabytes per gigabyte. So:
- A camera recording continuously at 2Mbps uses about 22GB a day.
- At 4Mbps, about 43GB a day.
- At 8Mbps, about 86GB a day.
Multiply by the number of cameras and the number of days you want to keep, and you have the drive size.
Worked examples
These use typical continuous-recording bitrates. Real bitrates vary with scene activity, lighting and settings, and night scenes with noise use more.
- A home with 4 cameras at 2Mbps: about 86GB a day. A 4TB drive holds about 46 days.