Optimal Column Width
A summary of research into the optimal width of columns (also known as "line length").
Researchers, Bruijn et al., discovered that human beings prefer shorter line lengths when reading content online because it appears more organised and easier to understand.
Reading a long line of type, for example full width of a desktop or laptop, quickly causes fatigue. The reader of the text must move his or her head at the end of each line and then search for the beginning of the next line.
If a casual reader gets tired of reading a long horizontal line, then they're more likely to skim the left edge of the text. If an engaged reader gets tired of reading a long horizontal line, then they're more likely to accidentally read the same line of text twice (a phenomenon known as "doubling").
According to prominent twentieth century Swiss typographer, Emil Ruder, if a line of text is too long the reader's eye will have a hard time focusing on the text. This is because the length makes it difficult to get an idea of where the line starts and ends. Furthermore it can be difficult to continue from the correct line in large blocks of text.
A width of between sixty and seventy characters is often referred to as the perfect measure. Derived from this range is the ideal range that all designers should strive for: 45 to 75 characters (including spaces and punctuation) per line for print. Many UX designers apply that rule directly to digital. I've found, however, that we can reliably broaden the range to 45 to 85 characters (including spaces and punctuation) per line for web pages.
Two other researchers, Dyson and Haselgrove, found that people comprehend shorter line lengths better than longer line lengths.
The problem is, to ensure maximum comprehension and the appearance of simplicity, the perfect line length ranges between 40 and 55 characters per line, or in other words, a content column that varies between 250 pixels and 350 pixels wide; this does depend on your choice of font size.
To determine line length for optimum readability, a good guideline is between 9 and 12 words for unjustified text. Fewer words may cause the sentence structure to break up, and may also result in too many hyphenations. Both of these reduce readability. Conversely, a line with more than 12 words can become tedious to read. Again, a reader can easily get lost when going from the end of one long line to the beginning of the next, and may inadvertently reread the same line, or miss a line or two.
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. So what's the downsides of violating this range?
Technical manuals and academic papers tend to be more densen. This is to convey the impression of complexity that might be undermined by a big, easy to read letters on the page. The pages of academic pages and published studies are densely packed with small fonts, but they still honour the rules of readability.
Early printed books used "justification" to get exactly the same amount of characters per line by breaking words with hyphens and varying the amount of spacing. This makes the page look better but its not always the best for readability. Automatic justification in programs like Word is even worse in terms of readability because Word creates gaps in the sentence which the brain has to work harder to read.
Line length can be measured by the physical length of the line (e.g. by adjusting margins) or can refer to the number of characters in a line. The number of characters per line can be varied by changing type size, but keeping the same physical length, e.g. 150 millimetres.
This article referenced Mary C. Dyson. Dyson wrote an academic article entitled : "How Physical Text Layout Affects Reading From the Screen".