Color Contrast (WCAG) Checker

About this calculator

This tool calculates the WCAG contrast ratio between a foreground and background color, a value from 1:1 (identical colors, no contrast) up to 21:1 (pure black on pure white), computed from each color's relative luminance. It then checks that ratio against the official AA and AAA accessibility thresholds — commonly 4.5:1 for normal text and 3:1 for large text under AA, with stricter minimums under AAA — to say whether a given text-and-background combination is actually readable enough to meet accessibility standards.

It is used by web designers and front-end developers checking a color palette before shipping it, since low-contrast text is one of the most common accessibility complaints and can fail legal accessibility requirements in some jurisdictions. Accessibility auditors also use this same calculation when reviewing a website or app for WCAG compliance, and design systems often bake AA-passing color pairs directly into their component libraries to avoid the problem entirely.