Color Contrast Checker
Compute WCAG contrast ratio & pass/fail.
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How it works
How it works
The WCAG 2.1 contrast ratio is computed from relative luminance in linear sRGB.
- Gamma expand sRGB to linear:
L = (c<=0.03928 ? c/12.92 : ((c+0.055)/1.055)^2.4). - Relative luminance:
0.2126 R + 0.7152 G + 0.0722 B. - Contrast ratio:
(L1+0.05)/(L2+0.05)with L1 ≥ L2.
Thresholds: AA 4.5 (normal text), 3.0 (large); AAA 7.0 (normal), 4.5 (large).
Privacy & Security
All calculations local.
Accuracy, Limits & Tips
Only hex input; no alpha channel.
Examples
- #000000 on #FFFFFF has 21:1 contrast.
Looking for broader guides and best practices? Visit the ToolsAreUs Blog for indexes (like the full tool list) and articles (e.g. secure password generation).