Work out how much hard drive storage your NVR/DVR needs — from camera count, resolution and how many days of footage you want to keep.
Uses the standard NVR storage formula (bitrate × seconds × hours × days × cameras, converted to GB) assuming H.265 compression. H.264 footage needs roughly double this storage for the same settings.
Storage (GB) = bitrate (kbps) × 3,600 seconds/hour × recording hours/day × retention days × number of cameras, divided by (8 × 1024 × 1024) to convert kilobits to gigabytes. This is the exact method used by CCTV manufacturers' own storage calculators.
Higher resolution cameras capture more detail per frame, which directly increases the bitrate needed to encode that detail — an 8MP/4K camera needs roughly 3× the storage of a 2MP camera recording the same hours and days, all else equal.
H.265 (also called HEVC) is the modern standard, roughly halving file size versus the older H.264 codec at the same visual quality — check your camera/NVR's actual codec, as this calculator assumes H.265.