If you’re reading this in a maximized browser on a wide-screen monitor, you may wonder why the margins are so big. The answer isn’t that this page is optimized for small displays. In fact, I asked the same question of LaTeX margins and I found an excellent answer on the LaTeX stackexchange that points out that the problem isn’t large margins, but large paper with respect to optimal line length.
The Elements of Typographic Style Applied to the Web states that line lengths are optimally between 45 and 75 characters including spaces. Emil Ruder suggests 50-60 characters in his book, Typographie. Emil goes on to say that readers are energized when their eyes move from the end of one line to the beginning of the next, as long as it doesn’t happen too frequently, and that this energy diminishes over the length of the line.
The Web Style Guide claims that research that reading slows as line lengths exceed the maximum width of about 12 words. With a space between each word and assuming 4 letters per word on average, this converts to about 12*4+11=59 characters per line.
You can use this bookmarklet to check the number of characters on a line in your browser. As of this writing, line lengths on this blog tend to be around 71 characters.
I would also like to take this opportunity to recommend Readability which converts any web page to a more readable version, and whose novel theme inspired the design of this blog.