Best Font Sizes for Readability: 16px Body, 1.5 Line-Height, 50–75 Char Lines (2026)

Recommended Font Sizes by Element

Why Font Size Is an SEO Concern, Not Just a UX One

Font size affects three measurable SEO signals:

1. Lighthouse "Document uses legible font sizes".This audit is part of Lighthouse's SEO category. It fails when more than ~40% of the page's text is under 12px. A failing audit lowers the SEO score reported in PageSpeed Insights.
2. Mobile usability.Google's mobile-first index evaluates every page primarily on its mobile rendering. Pages that require pinch-zoom to read are penalized as "not mobile-friendly" in Search Console's Mobile Usability report.
3. Engagement signals. Hard-to-read pages have shorter dwell times and higher pogo-sticking back to search results — both correlated with lower rankings (although Google does not confirm direct use of these signals).

How to Set Font Sizes Correctly

html { font-size: 100%; }     /* respects user setting (default 16px) */

body  { font-size: 1rem;       line-height: 1.6; }   /* 16px body */
h1    { font-size: 2.25rem;    line-height: 1.2; }   /* 36px */
h2    { font-size: 1.75rem;    line-height: 1.25; }  /* 28px */
h3    { font-size: 1.25rem;    line-height: 1.3; }   /* 20px */
small { font-size: 0.875rem; }                       /* 14px */

.article-content {
  max-width: 38rem;     /* ~65 characters at 16px */
  margin-inline: auto;
  line-height: 1.6;
}

<meta name="viewport" content="width=device-width, initial-scale=1" />

The Six Mistakes That Break Readability

p { font-size: clamp(1rem, 0.9rem + 0.4vw, 1.125rem); }

How to Audit Your Site's Typography

1. Run Lighthouse / PageSpeed Insights.Look for the SEO audit "Document uses legible font sizes". A failing audit lists the offending elements and what percentage of the page's text is below 12px.
2. Check Search Console > Mobile Usability.The error "Text too small to read" flags the exact URLs where Googlebot's mobile rendering found unreadable copy.
3. Use DevTools > Rendering > Emulate vision deficiencies. Combined with mobile device emulation, this surfaces low-contrast and small-font problems quickly.
4. Test browser zoom to 200%. WCAG 1.4.4 requires the page to remain functional. If layout breaks, your typography is using fixed pixel sizes where rems would scale cleanly.
5. Measure line length on the widest breakpoint. Open the article on a 1440px screen and count characters. If you're past 80, add a max-width to the prose container.

FAQ

Why does Google recommend 16px for body text?

16px has been the default body font size in every major browser since the early 2000s and is the size at which the "Document uses legible font sizes" Lighthouse audit passes. Google's mobile-friendliness guidance points at it as the minimum for body copy specifically because anything smaller forces pinch-zoom on phone screens.

Is 16px too small for long-form articles?

Not technically, but 18–20px is often more comfortable for sustained reading. Medium and many publishing platforms default to 18–21px for article body text. The lower bound is 16px; the upper bound is whatever still keeps lines under 75 characters.

What is the minimum font size that passes Lighthouse?

Lighthouse's "Document uses legible font sizes" audit passes when at least 60% of the page's text (by character count) is at least 12px. In practice, "at least 16px for body, 14px for captions, never below 12px" passes comfortably.

Should I use px, em, or rem for font sizes?

Use rem for typography. rem scales with the user's root font-size preference, which is critical for accessibility. em compounds (an em inside an em multiplies), which makes nested components hard to predict. px ignores user zoom entirely.

Does line-height affect SEO?

Not directly. But WCAG 2.2 SC 1.4.12 requires that pages support 1.5 line-height without breaking, and broken layouts at increased line-height count as accessibility failures — which feed into the broader page experience signal.

Why do my mobile forms zoom in when I tap an input?

Safari on iOS auto-zooms when a form field has font-size below 16px. The fix is to set font-size: 16px (or 1rem) on every input, textarea, and select. This is the most common and most under-diagnosed mobile UX bug in production sites.

How long should a line of text be?

50–75 characters per line is the optimum from Bringhurst's "The Elements of Typographic Style" — long enough to maintain reading rhythm, short enough that the eye finds the next line easily. 65 is the most-cited single number.

Is using user-scalable=no ever acceptable?

No. It violates WCAG 1.4.4 (Level AA), removes the user's ability to zoom for accessibility, and is widely flagged by accessibility audits. The viewport meta tag should always allow user scaling.