Here’s an interesting post on what the optimal line length is.
From the summary:
There are, however, some guidelines to help you out:
- 12 point size font as an absolute minimum,
- don’t condense letter spacing,
- when changing line length, change the leading accordingly,
- Remember: optimal is not necessarily fastest reading line length but is the size preferred by the users,
- think about the impact on line length and leading when changing font size,
- keep the text layout clean and uncluttered and use enough white space.