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
Some photographic still cameras such as DSLRs can exceed 5K resolution when capturing still images, but not when capturing video. For example, the Canon EOS 5D Mark IV announced in August 2016 has a maximum resolution of 67204480 pixels (around 30 megapixels in a 3:2 aspect ratio) which is used for high resolution still images, but it can only capture video at a maximum of 40962160 and a framerate of 30 Hz.