WCAG Contrast Ratio Explained: How to Check Text Readability in 10 Lines
The WCAG contrast ratio is a mathematics-based standard that measures whether text is readable against a given background color. The ratio is calculated by converting hex colors to linearized RGB values, computing relative luminance, and dividing the lighter luminance by the darker one, yielding a scale from 1:1 to 21:1. WCAG accessibility guidelines require a minimum ratio of 4.5:1 for normal text and 3:1 for large text at the AA level, with stricter thresholds at AAA. Approximately one in twelve people have some form of color-vision deficiency, making sufficient contrast important for a broad range of users. A live, library-free contrast checker demonstrating the full calculation has been published as part of the SolveFromZero project.
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