I use the WebAIM contrast checker: https://webaim.org/resources/contrastchecker/ https://webaim.org/resources/contrastchecker/ It's basically a measure of per

I use the WebAIM contrast checker: https://webaim.org/resources/contrastchecker/ https://webaim.org/resources/contrastchecker/ It's basically a measure of perceived brightness. The actual formula involves calculating the relative luminance of the background and foreground colors, where luminance is a value from 0 (darkest) to 1 (lightest), and using the formula (lighter_luminance + 0.05) / (darker_luminance + 0.05) So the highest possible contrast ratio in this system is 21:1.