Optimum Line Length

If you go entirely by empirical research, you will discover that from the first books printed in English to today’s paperback novels, there are about 65 characters per line in material that is meant to read immersively. Several studies have looked at the optimum reading line length in English and agree that for immersive reading experiences, around 65 characters per line is best. Even design books will tell designers to use the two-and-a-half alphabet line length as a guideline for best readability. But why is it?

An examination of the mechanics of the eye shows that there is a parafoveal angle of the eye that is approximately 12°. Within that, there is a foveal angle that is about three-quarters of a degree. The foveal angle is the amount of input into the eye that is sharply in focus. The parafoveal is the amount of information that is registered, but largely ignored by they eye as being slightly out of the direct line of sight. Beyond this 12° range we enter peripheral vision. The interesting thing is that this marks out the range of eye movement that can be done without engaging the neck muscles to turn the head as one reads. So, one might say that there are 16 chunks of sharp vision in the 12° range as the eye scans a line of type before returning to the beginning of the line.

But how much information can be acquired in each resting point. Some studies have shown that we can sharply see and register about 4–5 characters within the foveal fixation (coincidentally, the average length of an English word). What is not readily available in that information is whether the character recognition was based on a common book line of type or if it was scientifically arrived at by quantifying how much information the brain is able to comprehend from one foveal fixation point. It seems curious that the line length conveniently works out to 4 times 16 or 64 characters as the optimum.

Without getting into a criticism of what we base our opinions on, I think that there is an open question that arises out of the investigation that no one has broached. Is it the number of characters within the foveal range or the amount of information that is contained therein. If it were the number of characters, we should expect that there should be 4 or five Chinese characters in a fixation of the eye. But each Chinese character is an entire word. So where we have five characters to make up one word, the Chinese would find five words. Can the eye grasp that amount of information in a single fixation? Or does it imply that Chinese should be written with only 32–33 characters per line instead of 64–66?

I raise these as questions, acknowledging that a lot of work has been done on this subject, but not yet having found the exact universal algorithm that would translate typesize intuitively across cultures and script types. I’m not yet ready to propose an answer, even though I’ve proposed a couple patents on technology that would offer one solution. For here, it is enough to question.