Screen numbers explained
Sizes are in CSS pixels, the units web pages use. A phone with a 1170 pixel wide panel and a pixel ratio of 3 reports 390 CSS pixels. Multiply by the pixel ratio for the physical resolution. Browser zoom changes the ratio too.
Colour gamut says how many colours the screen can show: sRGB is standard, Display P3 is wider (most recent phones and Macs), Rec. 2020 is wider again.
Why sites read these values
To send images at the right size, use touch-friendly controls and honour your settings such as dark mode or reduced motion. The same values also help sites tell browsers apart without cookies, which is why browsers round some of them.
Questions
- Why does my screen size look smaller than advertised?
- Advertised resolution is in physical pixels; websites see CSS pixels after your system's scaling. 2560 pixels at 150% scaling appears as about 1707.