Estimate data for simultaneous streams.
Concurrent streams do not share bandwidth — each one needs its own, so three 6 Mbps streams require 18 Mbps of sustained capacity and consume three times the data. The peak bandwidth figure is the one that determines whether the connection can cope at all, and it is why a household that streams comfortably alone starts buffering the moment a second and third person join.
Concurrent stream load
Peak Mbps = streams x per-stream Mbps; GB per hour = peak Mbps x 3600 / (8 x 1024); period GB = GB per hour x concurrent hours x days
Around 1.5 to 2 times. Adaptive streaming needs room to buffer ahead, and other household activity competes, so a household with an 18 Mbps peak streaming need is comfortable at 35-50 Mbps rather than at 20.
No. Each device opens its own stream from the provider, so the content is transferred twice. Only a local multicast or a shared screen avoids that, and consumer streaming services do not use multicast.
Because the combined demand exceeds available bandwidth and the adaptive algorithms all drop quality or stall together. It is a capacity problem at the peak, not a total-data problem.