Color Contrast Checker

WCAG (Web Content Accessibility Guidelines) defines minimum contrast ratios: 4.5:1 for normal text (AA), 3:1 for large text (AA), and 7:1 for normal text (AAA).

Sufficient color contrast ensures text is readable for people with low vision or color blindness, and is a legal requirement in many jurisdictions under accessibility laws.

Relative luminance is a perceptual measure of brightness defined in WCAG 2.1. It linearizes the sRGB color components (R, G, B divided by 255) using a gamma correction formula and combines them as 0.2126R + 0.7152G + 0.0722B. The weights reflect human eye sensitivity — we perceive green most strongly and blue least.

Large text is defined as 18pt (24px) or larger for normal weight, or 14pt (approximately 18.67px) or larger for bold text. Large text has a lower AA threshold (3:1) because it is inherently more readable than small text at the same contrast ratio.

The tool suggests fixes by automatically finding the nearest shade of each color that passes AA. For text on white backgrounds, darkening the text color is usually the fastest fix. For text on colored backgrounds, either darken the background or lighten the text until the ratio reaches 4.5:1.

WCAG contrast ratios are a minimum baseline, not a guarantee. Some users with specific forms of color blindness may struggle even with passing ratios if the colors are in similar hue families (e.g., red and green). Testing with real users or using simulation tools for common color vision deficiencies provides deeper assurance.