Choose streaming quality for your data plan.
Rather than asking how much data a quality setting uses, this works backwards from the constraint: given an allowance and the hours you want to watch, what bitrate fits. Reserving data for browsing, calls and updates first is important, because streaming will otherwise consume the entire plan. The resulting bitrate maps directly onto the quality setting you should choose in the app.
Quality from a data budget
Available GB = budget - reserved; GB per hour = available / viewing hours; affordable Mbps = GB per hour x 8 x 1024 / 3600
Roughly 0.7-1 Mbps for 480p, 2.5-3 Mbps for 720p, 4.5-6 Mbps for 1080p and 16-18 Mbps for 4K. Newer codecs such as AV1 and HEVC reach the same quality 30-50 percent lower.
Because browsing, video calls, app updates and cloud backup still have to happen. Allocating the entire allowance to streaming guarantees running out before the cycle ends, usually at the least convenient moment.
Fixed, on a metered connection. Automatic mode raises bitrate whenever the connection allows, so a fast link means it will happily stream far above the level your allowance supports.