Controlling Line Length in CSS for Better Readability

Text that stretches across your entire screen is exhausting to read. Your eyes lose their place, comprehension drops, and readers abandon your content. Yet controlling line length in CSS remains one of the most overlooked aspects of web typography.

This article covers the research behind optimal line length, practical CSS techniques for implementation, and why the “rules” aren’t as rigid as you might think.

Why Line Length Matters for Reading Experience

When text runs too wide, readers face several problems:

• Return sweeps become difficult: Your eyes struggle to find the next line’s beginning
• Comprehension decreases: Wide text feels overwhelming and intimidating
• Reading motivation drops: Each new line provides a psychological boost—longer lines mean fewer boosts

Research from the Baymard Institute shows that 50-75 characters per line creates the optimal reading experience for body text. The Web Content Accessibility Guidelines (WCAG) sets an upper limit of 80 characters (40 for Chinese, Japanese, or Korean text).

But here’s what’s interesting: Mary Dyson’s research challenges the long-held belief that shorter lines are always better. Her findings show that readers can process words even when their eyes “undershoot” the beginning of a new line. This means longer lines don’t necessarily slow reading speed as much as we thought.

Modern CSS Techniques for Line Length Control

Using Character Units (ch)

The simplest approach uses CSS character units:

.content {
  max-width: 65ch;
}

One ch equals the width of the “0” character in your chosen font. This creates a relative measurement that scales with font size.

Responsive Line Length with clamp() and min()

For responsive designs, combine clamp() with viewport units:

.article {
  max-width: clamp(45ch, 90vw, 75ch);
}

This code:

• Sets a minimum width of 45ch
• Prefers 90% viewport width on smaller screens
• Caps at 75ch maximum on larger displays

For more complex scenarios, you can nest min() within clamp():

.article {
  max-width: clamp(45ch, min(90vw, 65ch), 75ch);
}

This ensures text remains readable on small screens while maintaining optimal line length on larger displays.

Container Queries for Context-Aware Sizing

.text-container {
  container-type: inline-size;
}

.text-content {
  max-width: min(100cqi, 65ch);
}

Container queries let you set line length based on the container’s size rather than the viewport, perfect for component-based designs.

Natural Line Length Through Layout Design

Sometimes CSS isn’t necessary. Strategic layout choices naturally constrain text width:

• Multi-column layouts: Split content into columns
• Sidebar designs: Place navigation or supplementary content alongside main text
• Card-based layouts: Contain text within defined boundaries
• Grid systems: Use CSS Grid to create natural content boundaries

These approaches often feel more organic than hard-coded width limits.

Accessibility and Special Considerations

Readers with Dyslexia

People with dyslexia often benefit from shorter line lengths—around 45-50 characters. Consider offering a “reading mode” toggle that applies tighter constraints:

.reading-mode {
  max-width: 50ch;
  line-height: 1.8;
}

Multi-Language Support

Different languages require different considerations:

• Asian languages: WCAG recommends 40 characters maximum
• Right-to-left languages: Ensure your line length CSS works with dir="rtl"
• German and compound words: May need slightly wider limits

Finding Your Optimal Range

Rather than following rigid rules, consider these factors:

1. Font choice: Wider fonts may need fewer characters per line
2. Font size: Larger text can handle slightly longer lines
3. Content type: Technical documentation might work with longer lines than marketing copy
4. Device context: Mobile readers tolerate shorter lines better

Test your line length CSS across devices and gather user feedback. What works for a blog might not suit an e-commerce product description.

Conclusion

Controlling line length in CSS improves readability, but optimal implementation depends on your specific context. Start with the 50-75 character guideline, use modern CSS functions for responsive behavior, and remember that accessibility needs may require tighter constraints. Most importantly, test with real users—the best line length is the one that helps your readers actually read.

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