This is a very common question with a very simple answer; it depends.
For those of you looking for a more complete answer I will go a little deeper. The amount of recording time the DVR can save is based on a few variables. They are the Hard Drive Size, Record Mode, Record Quality, Frame Rate, and Record Size.
Hard Drive Size: When it comes to the hard drive the bigger the drive the greater the storage capacity. Typical size for a basic drive should start at 500 gigabytes and can be as much as 2 terabytes. Depending on the DVR it can hold multiple drives for a stacked effect. Some machines can hold as many as 12 terabytes. That is a whole bunch of storage!
Record Mode: The mode you record in makes a big difference for the average user. The two most common options are 24 hour and motion only. 24 hour is exactly how it sounds. It never stops recording, which means it never stops filling hard drive space. Motion recording is great for locations with “downtime”. Businesses that operate from 9-5 will save a large amount of space during non business hours when there is nothing setting off the motion alarms triggers. I recommend motion in most every case. No motion equals no recording, which equals more record time.
Record Quality: This may seem a little silly but there are applications where it is not necessary to get high quality recording. However, I generally recommend the best quality setting for all cameras. When you lower the quality of the recording you are storing less data. Less data equals less storage and more record time.
Frame Rate (FPS): The average movie records and plays at 24 fps (pictures/frames per second). Real time recording for DVR systems is 30 fps. In most cases 15 frames a second looks pretty good but may miss some details that would be of great help in theft, slip and fall, and many other incidents. Unless storage time is a real problem I always recommend 30 fps. Basically, more frames equals more pictures and more pictures equals more data, which equals less record time.
Record Size: Similar to record quality, record size changes the amount data placed on the hard drive. In most cases the standard recording is done in (352 x 240 resolution) aka CIF. The industry uses this as the basis for all the formulas for recording time. In most cases CIF is a reasonable record size. The larger the frame, the more data, which equals less record time.
Now that you know more than you may have wanted to know about DVR recording let me tell you how the math works. In a typical scenario, a camera system will use about an average of 6 gigs of storage space per camera per day in motion mode. For 24 hour record it’s closer to 10 gigs per camera per day.
Motion – 4 cameras and 500g HDD = 6g x 4 cameras = 24g per day.
(Approximately 20 days)
24 hour – 4 cameras and 500g HDD = 10g x 4 cameras = 50g per day
(Approximately 12 days)