Typographers have known this for quite some time. It's called "measure" and it should be around 65-75 characters (according to the typographer's bible, The Elem

Typographers have known this for quite some time. It's called "measure" and it should be around 65-75 characters (according to the typographer's bible, The Elements of Typographical Style by Binghurst: http://en.wikipedia.org/wiki/The_Elements_of_Typographic_Style http://en.wikipedia.org/wiki/The_Elements_of_Typographic_Sty...)