Multiply the horizontal pixel count by the vertical count. A 1920 × 1080 picture has 2,073,600 pixels; 3840 × 2160 has 8,294,400; 7680 × 4320 has 33,177,600. These are frame dimensions, not file sizes or internet-speed requirements.
Start with both dimensions
A label such as 1080 p gives only the vertical count and scanning method. The common widescreen format is 1920 × 1080, but other widths exist. Use the dimensions shown in media information when accuracy matters, especially with cropped films, portrait recordings or nonstandard streaming sources.
Understand the multiplication
Doubling both width and height multiplies area by four. That is why 3840 × 2160 has four times as many samples as 1920 × 1080, rather than twice as many. The same relationship applies when moving from consumer 4K to consumer 8K dimensions.
Keep data calculations separate
Compressed video does not store every pixel as a simple uncompressed colour value. Motion prediction, chroma subsampling and codec settings change the data required. Calculate streaming data from bitrate and duration, not by multiplying the pixel count by a guessed number of bytes and treating that as a subscription’s bandwidth requirement. Use a separate bitrate-and-duration calculation when estimating a household data allowance.