Sample text at standard 16px size (normal).
Sample text at 24px bold (large).
Color contrast determines whether text is readable for users with low vision, color blindness, or in challenging viewing conditions. The WCAG (Web Content Accessibility Guidelines) define minimum contrast ratios for two compliance levels: AA (most legal requirements like the ADA in the US, EN 301 549 in the EU) and AAA (the higher bar, recommended where feasible). AA requires 4.5:1 contrast for normal text and 3:1 for large text (18pt+ or 14pt bold+); AAA requires 7:1 for normal and 4.5:1 for large. This tool computes the exact contrast ratio between any two colors and reports pass/fail for both standards at both text sizes. All math runs in your browser using the WCAG-defined relative luminance formula.
Frequently asked questions
The relative luminance of the lighter color plus 0.05, divided by the relative luminance of the darker color plus 0.05. Pure white on pure black is 21:1. The WCAG-required minimum is 4.5:1 for AA-compliant normal text. The closer to 1:1, the harder text becomes to read. The tool computes this ratio exactly from the WCAG specification.
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