The goal of having good vertical rhythm is to provide a comfortable and engaging reading experience for our users. The challenge is, how do we know when we’ve achieved it, besides our design instincts? And how do we maintain the rhythm when the content changes?

Using relative units is essential to responsive design, and considering the infinite scenarios in which web content can be viewed, it is almost always necessary to be responsive by default. Let’s demystify when to use rems, ems, and pixels.