Enter the relative luminance of the lighter color and relative luminance of the darker color into the calculator to determine the contrast ratio.
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Contrast Ratio Formula
The following formula is used to calculate a contrast ratio.
cr = (L1+.05) / (L2 + .05)
- Where cr is the contrast ratio
- L1 is the relative luminance of the lighter color
- L2 is the relative luminance of the darker color
Contrast Ratio Definition
What is a contrast ratio? A contrast ratio is defined as the difference in luminance between two different colors that place adjacent to each other.
Example Problem
How to calculate contrast ratio?
- First, determine the relative luminance of the light color.
The relative luminance is found to be .215.
- Next, determine the relative luminance of the darker color.
For this example, the luminance is found to be .125.
- Finally, calculate the contrast ratio.
Using the formula, the contrast ratio is found to be (.215+.05) / (.125 + .05 ) = .220/.130 = 1.692 : 1.
