How to Choose Fonts for Readability, Not Just Looks
A font that looks beautiful in a specimen can be painful to read at length. These are the criteria that actually predict readability. Readability is the job of body text, and most font choices are made on appearance instead. A typeface that looks elegant in a large specimen often becomes tiring after three paragraphs of small text. After choosing fonts for reading-heavy projects and getting feedback from real users, I have a short list of criteria that predict whether a font will read well at length. X-Height Is the Strongest Signal X-height is the height of lowercase letters, and it is the single best predictor of body-text readability. Fonts with a large x-height, like Inter, Source Sans, or Roboto, keep lowercase letters open and distinct at small sizes, which helps the eye recognize word shapes quickly. Fonts with a small x-height, common in classic serifs, can look refined in a heading but become hard work in long passages because the lowercase letters close up. When I evaluate a font for body text, the first thing I check is the x-height relative to the cap height. A ratio that favors the x-height is a good sign. I then read a full paragraph at the target size. If I have to slow down or reread sentences, the font fails the test no matter how good it looks in isolation.