Line Length: The problem and the solution
Line length is defined by practicaltypography.com as the distance between the left and right edges of a text block. All sites must have it, because monitor can only go so far, and a page can only go so far in one direction before it has to stop. The major problem comes in however, via subtle changes. When the line only has so many words or characters, or the font size is off for some reason, it messes with our ability to read through a page well. Simply put, it can heavily damage the user interface and the user experience, preventing users from ever wanting to come back to your site. It's a fine line and easy to slip and fall down into. So how can we fix this?
The Solution
The solution varies, but generally falls within 2 main categories: Character amount per line, and font size. If a line is too wide or narrow, it will mess with the user's perception. Baymard Institute defines the optimal line length as 50-75 characters per line. Other sites, like kickpoint.ca, suggest wider ranges, but still close to that range is a good place to start. Font size is also highly important. smashingmagazine.com defines a suitable font size as somewhere between 13-18 pixels depending on the font for a laptop or desktop monitor. However, smaller devices must come into play. When factoring that in, font sizes may have to change. Their site then recommends somewhere between 12-17 pixels depending on the font.
Making a webpage that is perfect for the average user to read is not meant to be easy, but with the keys of trying to limit a line to a certain number of characters, or changing the font size, one can make their website much more appealing.