When does WCAG AA accept 3:1 contrast for text? The large text rule explained

Success Criterion 1.4.3 lists large text as an exception to the 4.5:1 rule: "Large-scale text and images of large-scale text have a contrast ratio of at least 3:1." Large-scale means at least 18 point, or 14 point bold. Converted to CSS pixels, 18 pt is 24 px and 14 pt is about 18.7 px, since a point is 1/72 inch and a CSS pixel is 1/96 inch. In CSS, bold is font-weight 700. The Understanding page adds a note: "Fonts with extraordinarily thin strokes or unusual features and characteristics that reduce the familiarity of their letter forms are harder to read, especially at lower contrast levels." A hairline display face at 24 px may need more than 3:1 to read well.

Take #949494 on white, which gives 3.03:1. It passes the 3:1 large text rule and fails 4.5:1 for normal text. For body text, try #767676. On white it gives 4.54:1, and that passes 4.5:1 for normal text.

What counts is the size and weight the page renders. Body text at 16 px (12 pt) is normal text, even with a heavy heading right above it, because each run of text gets its own size and weight.