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readability-line-length

Set line length (measure) for prose — capping the maximum width of body text so lines stay in the 45–75 character range that supports comfortable sustained reading. Use when designing article layouts, documentation, email templates, dashboard copy, or any container that holds paragraphs of prose. Line length is the most fundamental readability decision because it directly affects the reader's eye movement; lines that are too long or too short both cost reading comfort.

plugins/HDeibler/universal-design-principles/plugins/perception-and-hierarchy-principles/skills/readability-line-length/SKILL.md

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# Readability — line length (measure)

Line length, also called *measure* in typography, is the number of characters per line. It's the most fundamental readability decision because it directly affects the reader's eye movement: at the end of each line, the eye must jump back and find the start of the next line, and the difficulty of that jump scales with line length.

The recommended range, established by centuries of book typography research and confirmed by modern reading studies: **45 to 75 characters per line for body prose**, with 60–66 as the sweet spot for most use cases.

## Why line length matters

Two failure modes bracket the comfortable range.

**Too long (>75 characters per line).** The eye must travel a long distance between line ends. The reader can lose their place — find the wrong line on the way back, or read the same line twice. Reading slows. Fatigue accumulates faster.

**Too short (<45 characters per line).** The eye has to jump too frequently. Each line break interrupts the cognitive thread. Words at the line ends are often hyphenated awkwardly. Reading feels stuttering rather than flowing.