This depends on the number of cameras recording at the same time and the level of quality/detail they record at. This will also depend on how big your hard drive is. If you require us to spec up a system to record for a certain amount of time please contact our support team. With our recorders, you can also save recording space by only recording when motion is detected. Simple in short you tell us how long you need it to record for and we will put the correct size hard drive in.