What is the optimal line of text length for good readability? What this implies?

We should aim for optimal line lengths of 45 to 75 characters, including spaces, in order to provide good text readability. If lines are longer, we may want to adjust the margins or introducing columns; and we may want to increase font size as well.

Having this in mind will help us decide when the breakpoints in a RWD will occur.

Tip: put a span enclosing the 45th to 75th character, color its background, and test.