Document doesn't use legible font sizes

Font sizes smaller than 12px are often difficult to read on mobile devices, and may require users to pinch-to-zoom in order to display the text at a comfortable reading size. Lighthouse flags pages with illegible font sizes:

Lighthouse audit showing page has illegible font sizes
Fig. 1 — Font sizes illegible

What causes this audit to fail

When a page fails the audit, Lighthouse lists the results in a table with 4 columns:

  • Source. The source location of the CSS ruleset that is causing the illegible text.
  • Selector. The selector of the ruleset.
  • % of Page Text. The percentage of text on the page that is affected by the ruleset.
  • Font Size. The computed size of the text.

Each SEO audit is weighted equally in the Lighthouse SEO Score, with the exception of the manual audit, structured-data audit. Learn more in Lighthouse Scoring Guide.

How to fix illegible fonts

Aim to have a font size of at least 12px on at least 60% of the text on your pages. Learn more in Fix small font sizes.

Text is illegible because of a missing viewport config

If Lighthouse reports Text is illegible because of a missing viewport config, add a <meta name="viewport" content="width=device-width, initial-scale=1"> tag to the <head> of your document.

See also Has a <meta name="viewport"> tag with width or initial-scale.

More information

Illegible font sizes audit source

Last updated: Improve article