In 2017, 77% of Americans own a smartphone, a phenomenal increase from just 35% in 2011 (source: Pew Research Center Mobile Fact Sheet). And we are not just talking about a single screen size here! There are a multitude of screen sizes to consider from different versions of iPhones, android. And outside of smartphones, you probably want to consider iPads, tablets, desktops, tvs, to name a few.