Not sure if there is already a topic on this, but I think it deserves one. I guess most people don’t think much about the optimal line length when they are considering lay out, at least, I used not to care about this, untilI began working with a more professional document preperation system (LaTeX).
I was suprised that the standard setting there is too have very wide margins, which felt to me like a waste a paper, until I found a post on stackexchange, which convinced me of the following:
Something similar is true for our screens, they are way too wide, very cool for watching movies, but not at all useful for reading text.
The optimal line length for your body text is considered to be 50-60 characters per line, including spaces (“Typographie”, E. Ruder). Other sources suggest that up to 75 characters is acceptable. Link
Well, 50-60 characters a line is not much at all, it would be even hard to get only 75 character in each line, and still let discourse look natural on wide screens, but I think it is something to consider. I only realized how much better those 50-75 characters line read, when I compared reading a normal book with 60 characters, and printed this book out in A4 paper having 110 charachters on each line. It is really huge difference in readability.
Currently, discourse (at least meta.discourse.org) has around 110 characters per line. I played around a bit, and the image below has around 70-80 characters per line:
Sorry for the bad quality of the image, not sure how to make good quality screenshot with my macbook retina.