Estimate data used by security cameras.
Cloud-connected cameras are the heaviest sustained upstream load in a home, because they run continuously rather than in bursts. Four cameras at 2.5 Mbps recording around the clock would upload well over 3 TB a month; motion-triggered recording cuts that to whatever fraction of the day actually contains movement, typically 10-20 percent. That duty cycle is the single most important number in the calculation.
Camera upload with motion duty cycle
GB per camera-hour = Mbps x 3600 / (8 x 1024); continuous daily = per camera-hour x hours x cameras; actual daily = continuous x duty cycle
Roughly 1-2 Mbps for 1080p with H.265, 2-4 Mbps with older H.264, and 4-8 Mbps for 4K. Higher frame rates and busy scenes with moving foliage push variable-bitrate encoders toward the top of the range.
Yes for the upload. A local NVR keeps footage on site and only uses internet data when you view a stream remotely, which is why local storage is the standard answer for a capped or slow upstream connection.
Motion detection triggers on more than people: passing cars, pets, moving shadows and swaying branches all count. Tuning detection zones and sensitivity usually halves the recorded duty cycle without missing genuine events.