Pixels are only part of the picture
720p, 1080p and consumer 4K describe different image sizes. Compression, source quality and the display also influence what you see. A crisp poster or a large image on a title page does not establish the resolution of the available video.
Look at the real edition
Use the quality menu and edition details of the viewing service. A plan or device may support only some of the options. For a long film on a limited connection, a stable supported setting is usually less frustrating than repeatedly forcing a higher level that cannot keep up.
WEB-DL, BluRay and HEVC
Source and codec labels tell different stories. A source description says where an edition originated; a codec says how it was compressed. Neither is a guarantee that a particular copy is complete or visually excellent. See the format guide for the distinction.
Compare the data cost
Resolution has no single fixed file size. Use the data calculator with the running time and combined bitrate you want to compare. Its estimate is not a speed test, a stream measurement or a download offer.