A line of text should be about 60–90 characters long. Higher than that, and a lot of people will have trouble keeping track of which line they're on. However, t

A line of text should be about 60–90 characters long. Higher than that, and a lot of people will have trouble keeping track of which line they're on. However, that's only the width of the body text. If you have sidebars or figures or such, those can take up more horizontal space as needed. It's true that a user can set the width of their browser to make your text flow to an acceptable width. However, most browser windows contain multiple tabs, and it's annoying to switch between a bunch of tabs that each require the window to be resized for an optimal experience.