Choose a family data plan by usage.
Family plans pool data, so sizing by the average per line understates the requirement whenever one person uses far more than the rest. Building the pool from the heaviest line plus the average of the others captures that skew. The heaviest-line share is the diagnostic figure: when one line takes more than about 40 percent of the pool, moving that person to their own unlimited line is often cheaper than upgrading the whole plan.
Pooled plan sizing with skew
Baseline pool = heaviest line GB + (lines - 1) x average GB; recommended = baseline x (1 + headroom); per line = recommended / lines
Because household usage is heavily skewed. If one teenager uses 22 GB and three others use 3 GB each, the average is 7.75 GB — but sizing at 31 GB from the average misses that the distribution matters for whether any single line can be throttled.
Typically when one line exceeds roughly 40-50 percent of the pool. At that point you are buying pool capacity for everyone to serve one person, and a single unlimited line plus a smaller pool for the rest usually costs less.
Some do. Providers increasingly apply a per-line soft cap inside the pool, so a single heavy user gets slowed even while the pool has capacity left. Check whether your plan has that before sizing purely on the total.