Viewing distance

Screen size alone tells you surprisingly little about how to design an interface. A 50-inch HDTV and a 5-inch Galaxy S4 can both display 1920×1080 pixels, but one is 10 feet away from you and the other is about a foot from your face. Same pixels, very different experience.

So what are the typical distances? TVs are about 10 feet away, laptops about 2 feet, tablets about 18 inches, and smartphones about 12 inches. One study I shared put average smartphone web viewing at 32 centimeters (12.6 inches). That distance has an obvious impact on legibility for font and image sizes, but it also affects other design elements like contrast.

My favorite example is Netflix. They sized movie box art in physical dimensions based on distance: 1 inch on a phone, 1.75 inches on a tablet, 2.25 inches on a laptop, and 5.25 inches on a TV. I really wanted there to be a magic formula like half an inch per foot, and it almost works if you treat smartphones as 10 inches away instead of 12. The payoff is big. Netflix runs on over 500 different devices, but by thinking in viewing distance they can boil that list down to about four experiences.

None of this is new, by the way. The London Underground's sign manual has accounted for viewing distance when sizing elements for a very long time. And it gets weirder with devices like Google Glass, whose projected screen is the equivalent of a 25-inch HD screen viewed about eight feet away. That's why Glassware cards look a lot more like a screen on a newsroom wall than a shrunken web page.

Worth noting: most of this is from talks I gave around 2013 and 2014, so the device list is a bit dated. But the principle holds. Viewing distance is one part of user posture, and combined with input types (like a TV's D-pad vs. touch on a phone), it can change an interface in big or small ways even when screen size stays the same.

Put simply: design for how far away people are, not just how many pixels they have.