WCAG Contrast Checker

WCAG 2.1 Level AA requires a minimum contrast ratio of 4.5:1 for normal text (under 18pt / 24px) and 3:1 for large text (18pt bold or 24px regular and above). Level AAA raises the bar to 7:1 for normal text and 4.5:1 for large text.

The contrast ratio uses the relative luminance of two colours. The formula is (L1 + 0.05) / (L2 + 0.05), where L1 is the lighter and L2 is the darker. Luminance is computed from linearised sRGB values weighted by the human eye sensitivity to red, green, and blue.

Large text is defined as 18pt (24px) or larger at regular weight, or 14pt (approximately 18.66px) or larger at bold weight. Large text has a lower contrast threshold because its larger size makes it inherently easier to read.

WCAG 2.2 uses the same contrast ratio formulas and thresholds as WCAG 2.1 for text. The 4.5:1 and 3:1 requirements for AA, and 7:1 and 4.5:1 for AAA, are identical. This tool covers both versions.

Colour blindness changes which colours a person can distinguish, but does not necessarily change the luminance contrast ratio. However, colours that look different to typical vision may appear identical under colour vision deficiency. This tool simulates protanopia, deuteranopia, and tritanopia so you can check both the visual appearance and the simulated contrast ratio.

AA is the minimum recommended level for most web content. AAA is the enhanced level for maximum accessibility. AAA requires higher contrast ratios (7:1 for normal text vs 4.5:1 for AA). Most accessibility guidelines and legal requirements reference AA as the baseline.