The importance of copy width

Have you ever been reading a webpage (or some books) and your eyes start getting tired or you can’t remember what you just read, even if it’s the middle of the day or an interesting topic? There could be many factors at play but one people rarely consciously notices is content width. The length of a text line can have a real effect on how hard your brain has to work just to get through a paragraph.

Ancient Knowledge

If you’ve ever seen a medieval Bible, you’ll notice there’s a lot of white space. The margin-to-text ratio was often 50/50. This wasn’t merely for aesthetics. Medieval scribes understood that reading is work. They would memorize passages, and whitespace and narrow columns facilitate that. When Gutenberg invented the printing press in 1455, he maintained those generous margins. They weren’t simply a byproduct of hand-written scripts.

Modern Studies

In 1929, researchers Miles Tinker and Donald Paterson tried to prove it with data. They timed participants on how quickly they read and concluded that the optimum length is about 50-75 characters . When a line of text is too wide, your eyes have to work harder to jump from the end of one line to the beginning of the next. Researchers call this the “return sweep.”

Here’s what the research found:

• Too narrow (under 40 characters): Your eyes jump so frequently that it feels choppy. You lose flow and have to re-read more.
• Too wide (over 100 characters): Your eye has to travel too far. You lose your place and have to search for where the next line starts. This is mentally exhausting.
• Just right (50–75 characters): You fall into a rhythm. Your eye naturally knows where to go. Reading feels effortless.

In practical terms: a comfortable line length on desktop is somewhere around 600–800 pixels wide for your main content. For context this WordPress theme’s default content-width is ~780px. That might seem narrow if you’re looking at a full-width design, but that’s kind of the point. Your brain doesn’t actually want to read across the entire width of your monitor.

I know what you’re thinking: “but that study is 100 years old.” True, it’s old and may have had some flaws. But we have more modern studies on this subject, and they’ve returned interesting results. Some corroborate the original findings, while others are inconclusive or outright reject the speed claims. But the body of research continues to recommend that line length should not exceed around 70 characters per line.

Why Line Width Matters

So why do so many people experience difficulty with longer text? Because reading is a cognitive task, not just a visual one. When your visual system works overtime, it leaves less mental energy for actually understanding what you’re reading.

There might be some doubt about line-width affecting reading speed. But what most research agrees on is that narrow text (and whitespace) decreases our cognitive load, leading to better reading comprehension and recall.

Seems like those ancient scribes were onto something.

Accessibility

Also worth noting that most studies concluding line-width has no effect on reading speed did not control for neurodivergence. People with ADHD or dyslexia have shown to struggle less when their eyes don’t need to make large jumps on a page.

So if nothing else, making your website more accessible should be enough to convince you.

References

• Shorter Lines Facilitate Reading in Those Who Struggle
• Examining the Research Methods Used by Legibility Legends Tinker and Paterson
• The Forgotten Research of Miles Albert Tinker
• Margins – Medieval Books
• Bible Typography and Readability
• The Effect of Font Width on Eye Movements During Reading
• Optimal Line Length in Reading: A Literature Review — Visible Language
• An Eye-Movement Exploration into Return-Sweep Targeting During Reading — Slattery et al.