Every pair in the palette, in one pass
Auditing a design system is rarely about one pair of colors. It is about how everything you ship combines with everything else. Enter 3 to 8 colors and this page lists the contrast ratio for every possible pair, with the 3 : 1, 4.5 : 1 and 7 : 1 thresholds marked on each row. Eight colors produce 28 pairs on a single screen. Judging a single pair, or working out the smallest adjustment that fixes a failing one, belongs to separate tools.
How it is computed and the thresholds
Relative luminance follows the W3C WCAG definition. Each channel is divided by 255, linearized about the 0.04045 threshold, weighted by 0.2126, 0.7152 and 0.0722, then the lighter and darker luminance each get 0.05 added before dividing. The thresholds are 4.5 : 1 for AA normal text, 3 : 1 for AA large text, 7 : 1 for AAA normal text, 4.5 : 1 for AAA large text and 3 : 1 for non-text user interface components. Large text means 18pt and above, or 14pt and above when bold. Meeting the threshold counts as a pass, so 4.50 : 1 passes AA. The specification reference is current as of October 2026.
Limits
Each verdict uses the unrounded ratio, as WCAG requires, and the table shows it truncated to two decimals so a value such as 4.4994 reads 4.49 and fails. A contrast ratio does not stand in for a real screen with its own font sizes, weights and transparency, and this page does not judge color vision deficiency safety.
Frequently Asked Questions
It passes. The requirement is 4.5 : 1 or more, so the boundary value is included. This page judges on the same two decimal value it prints, so the number and the verdict never contradict each other.
The 3 : 1 column covers AA large text and non-text interface components such as buttons and input borders. The 4.5 : 1 column covers AA normal text and AAA large text. Those grades share the same number, so the columns are merged.
Black has a relative luminance of 0 and white of 1. Adding 0.05 to each and dividing gives 1.05 over 0.05, which is 21. That is the highest a contrast ratio can go, and a color against itself gives the lowest, 1 : 1.