CCTV Storage Calculator

A security recorder fills its disks at a rate set by the cameras, and the retention you promise decides how much space to buy. Run out and the oldest footage is overwritten sooner than expected, usually when an incident needs it. The page turns camera bitrate, count and retention into terabytes.

The arithmetic

A video stream’s bitrate is the bits written per second. Multiply by the number of seconds recorded and divide by eight to get bytes. At 2 Mbit/s a camera writes 250,000 bytes per second, which is 21.6 GB in a full day of 24 hours. Multiply by the number of cameras and days to keep, and you have the total. The calculation uses decimal units, as disk makers do, and shows TiB too for software that reports binary units.

What affects the bitrate

Codec: H.265 typically needs about half the bitrate of H.264 at similar quality. Resolution and frame rate: more pixels and frames mean more data. Scene: a static hallway compresses well, a busy street or noisy night image does not, and constant bitrate versus variable bitrate settings change the pattern. The preset bitrates on the page, 4, 2, 3 and 6 Mbit/s, are examples that show how the totals scale, and the page says clearly that real cameras vary. Look up the actual bitrate on the camera’s status page for an accurate figure.

Motion recording and hours per day

“Recording hours per day” and “share of time actually recorded” cut the total when you do not record around the clock. Motion-triggered recording at 25 percent of the time needs about a quarter of the storage, but only if the cameras are triggered as often as you assume; false triggers from insects, shadows and headlights push it up. Many recorders also keep a continuous low-quality stream plus motion clips at full quality, which is a different mix and should be added up separately.

A worked example

The preset “8 cameras, 30 days” uses the 1080p H.265 starting point of 2 Mbit/s per camera. Each camera writes 21.6 GB per day, so the total for 8 cameras over 30 days is 5.18 TB (4.71 TiB). All cameras together load the network with 16.0 Mbit/s, which is well within a 100 Mbit/s switch port. Adding the default 20 % headroom, the page recommends 6.22 TB. In practice you would round up to the next standard disk capacity.

Limits

RAID overhead comes on top: a mirrored or parity array needs more raw disk than the figure shown, which the RAID Calculator works out. The page does not include audio, thumbnails, system files or the file system’s own overhead beyond the headroom you choose. It cannot predict a camera’s variable bitrate, so validate with a trial recording. Power for the cameras is covered by the PoE Power Calculator.

Reducing storage without losing evidence

Several settings cut the total without removing the footage that matters. Lowering the frame rate at night or in quiet areas, using H.265, capping a variable bitrate, and recording the main stream only on motion while keeping a low-resolution sub-stream continuously all reduce the figure. Many recorders can also keep a few seconds of video before each trigger, so motion recording still captures the start of an event. Change one setting at a time in the calculator to see what each is worth before you apply it to the cameras.

Related tools

• RAID Calculator adds redundancy overhead to the storage plan.
• ZFS Capacity Calculator plans a ZFS pool for the same data.
• PoE Power Calculator checks the switch can power the cameras.
• Byte Converter converts between GB, TB and TiB.