[...] getting closer to a 4K TV, as the smaller pixels allow you to do [...] Standards body the International Telecommunications Union recommends sitting at least 1.5 times the height of the screen away from a 4K TV (so as not to see distracting pixels) and three times the screen's height away from an HDTV.
For a 55-inch (1.4 m) TV, like the entry-level models from Sony and Samsung, that comes out to a little more than 3 feet (0.9 m) for 4K, or close to 7 feet (2.1 m) for HD. [...]