Definition
Colour contrast
The brightness ratio between text and its background. Sufficient contrast is required for readability (a very common WCAG criterion).
Colour contrast measures the brightness difference between text and its background. WCAG AA require a ratio of at least 4.5 to 1 for body text, and 3 to 1 for large text.
Insufficient contrast is one of the most frequent problems. It is fixed by adjusting colours, without touching the page structure.
Frequently asked questions
What counts as large text?
Text of at least 18 points, or 14 points in bold, which corresponds to about 24 pixels and 18.66 pixels. Below that size, the required ratio rises from 3 to 1 up to 4.5 to 1.
Does contrast concern anything other than text?
Yes. Interface elements such as field borders, meaningful icons and focus indicators must reach 3 to 1 against their surroundings. This is a separate criterion from the text one, and it is often overlooked.
See also
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