Estimate total data needs for a household.
Household data is dominated by video, so the estimate is built around it: people x hours x the per-hour rate for the resolution they watch, times 30 days. Everything else — browsing, video calls, game downloads, OS updates — is added as a single monthly figure because it is far smaller and far less predictable. The suggested plan adds 25% headroom and rounds up to a typical 50 GB step, because exceeding a cap usually costs more than the next tier up.
Streaming
GB = people x hours per day x GB per hour x 30
Suggested plan
ceil(total x 1.25 / 50) x 50
Four times the pixels plus HDR metadata means roughly double to triple the bitrate of 1080p — about 7 GB per hour against 3. One 4K viewer can outweigh the rest of the house.
No. Speed and volume are independent: a faster line delivers the same file sooner. Only what you actually stream or download counts against a cap.