All these different resolutions for all these different devices. It can be pretty confusing and intimidating when you try to understand how they work. Is a pixel a pixel or isn't it? This can be mindblowingly complex. But here's what you should basically know: If you set the meta viewport to width=device-width,initial-scale=1 all devices translate the units you use in your CSS to usable formats on the screen. That is, if your CSS units are sensible in the first place. This means that a square of 40x40 pixels can be handled with fat fingers on every device. And this means that a 16px (or 1em) font-size is perfectly readable.