# Contrast ratio

The lightness difference between text and its background, as a ratio from 1:1 to 21:1.

**Source:** “of at least 4.5:1, except for the following” [Understanding SC 1.4.3: Contrast (Minimum) (W3C)](https://www.w3.org/WAI/WCAG22/Understanding/contrast-minimum.html)

See also: [WCAG](/reference/glossary/wcag), [Conformance level](/reference/glossary/conformance-level), [Target size](/reference/glossary/target-size).

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Published 2026-10-29. Web page: https://www.mackenziebowes.com/reference/glossary/contrast-ratio