Measure & Line Length: The 45–75 Character Rule

The horizontal length of a text block is called its measure. Measure is one of the most critical factors in reading comfort:

• Too Wide (> 85 characters): The reader's eyes must travel a wide distance across the screen. When reaching the end of a line, the brain struggles to track back and locate the beginning of the next line, leading to fatigue and lost focus.
• Too Narrow (< 35 characters): The eye has to jump back and forth constantly, interrupting reading flow and creating awkward hyphenations.

The Golden Measure: Optimal body text measure is between 45 and 75 characters per line (including spaces). In CSS, this is achieved using character units: max-width: 65ch;.