Readability: the Optimal Line Length

As we refine our methods of responsive web design, we’ve increasingly focused on measure (another word for "line length") and its relationship to how people read.

The popularization of the "ideal measure" has led to advice such as "Increase font size for large screens and reduce font size for small screens." While a good measure does improve the reading experience, it’s only one rule for good typography. Another rule is to maintain a comfortable font size.

How People Read

People read online text to serve their own needs: to find the information they seek, to discover new ideas and to confirm their notions about life.

PEOPLE READ IN THREE WAYS

In 2006, the Nielsen Norman group released images of heat maps from eye-tracking studies. The areas where people looked at the most while reading are red, areas with fewer views are yellow, and the least-viewed areas are blue. As you can see below, the red and yellow areas form three variations of an F-shaped pattern. These variations aren’t surprising because people read in three different ways.

People read casually, skimming over text, reading words and sentences here and there to get a sense of the content. The heat map below shows the eye movements of someone casually reading about a product. The reader spent time looking at the image of the product, reading the first couple of sentences, then scanning through the bulleted list.

NB.
1vw = 1% of viewport width.

The vw unit is not supported in IE8 and earlier.