Estimate data used streaming in HD.
1080p streaming sits at roughly 5 Mbps on most services, which works out to about 2.2 GB an hour — around a third of what the same content costs in 4K. Framing the result against your allowance rather than as a bare gigabyte figure answers the question people actually have: how many hours of viewing the plan supports before the cap becomes a problem.
HD data against an allowance
GB per hour = Mbps x 3600 / (8 x 1024); total GB = GB per hour x hours per day x days; hours supported = allowance / GB per hour
About 2.2 GB at 5 Mbps. Services vary: Netflix quotes roughly 3 GB an hour for HD, YouTube 1080p at 60 fps can reach 4 GB, and heavily optimised services using newer codecs come in under 2 GB.
Usually. It uses roughly a third of 4K's data while looking nearly identical on screens under about 50 inches at normal viewing distance, which is why it is the default recommendation for metered connections.
Adaptive bitrate. Services push higher bitrates when the connection allows, so a fast link may stream well above the nominal figure. Setting the app's quality to a fixed level rather than automatic makes usage match the calculation.