Estimate data used watching streams.
Streaming data is driven almost entirely by resolution. Standard definition runs under a gigabyte an hour, full HD around three, and 4K near seven — a tenfold spread for the same content. Multiplying by simultaneous devices matters because each stream is a separate transfer, so a household watching two 4K streams burns fourteen gigabytes an hour.
Session data
Session GB = hours x GB per hour for the quality x devices streaming
Allowance impact
Share of allowance = session GB / monthly allowance x 100
Dropping from 4K to 1080p more than halves consumption, and capping quality on mobile devices where the difference is barely visible saves more again. Most services expose a per-profile data setting.
Barely by comparison. Music at high quality is roughly 0.15 GB an hour, about one twentieth of a 1080p video stream.