4к бывает разное
My screen
Sizes
CSS device-width : 1920px+
CSS device-height : 1080px+
JS screen.width : 5760px
JS window.innerWidth : 5750px
JS body.clientWidth : 5733px
JS screen.availWidth : 5760px
Pixel ratio
CSS pixel-ratio : 1
JS pixel-ratio : 1.0000
Resolution
Resolution (dpi) : 96.00dpi
Resolution (dppx) : 1.00dppx
Resolution (dpcm) : 37.80dpcm
Misc
Root font size : 16px
Orientation :
Device Aspect-Ratio : 5.33