It’s easy to understand the difference between font-size units when you see them in action. Generally, 1em = 12pt = 16px = 100%. When using these font-sizes, let’s see what happens when you increase the base font size (using the body CSS selector) from 100% to 120%.
UX design is no longer about designing for a screen, but about designing for the integrated context. When we talk about empathy and our connected experiences, we're talking about something much larger than an Internet of Things. It's really the Experience of Things--everything that we use and interact with in our daily lives is starting to build a computing mesh around us.
Line height (in pixels) ÷ body copy font size (in pixels) = 1.48
1.5 is commonly recommended in classic typographic books, so our study backs up this rule of thumb. Very few websites use anything less than this. And the number of websites that go over 1.48 decreases as you get further from this value.