4K resolution
As noted above, DCI 4K is 40962160, while 4K UHD is 38402160, producing a slight difference in aspect ratio rather than a significant difference in resolution. Traditional displays, such as LCD or OLED, are 3840 pixels across the screen, with each pixel being 1/3840th of the screen width. They do not overlap—if they did, they would suffer reduced detail. The diameter of each pixel is basically 1/3840th of the screen width or 1/2160th of the screen height - either gives the same size pixel. That 38402160 works out to 8.3 megapixels, the official resolution of 4K UHD (and therefore Blu-ray UHD discs).
5K resolution
On April 14, 2008, Red Digital Cinema Camera Company launched one of the first cameras capable of video capture at 5K resolutions. Red Epic uses the Mysterium X sensor which has a resolution of 51202700 and can capture at a framerate of up to 100 fps. Cameras with 5K resolution are used occasionally for recording films in digital cinematography.