Enter the relative luminance of the lighter color and relative luminance of the darker color into the calculator to determine the contrast ratio.

## 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?

1. First, determine the relative luminance of the light color.

The relative luminance is found to be .215.

2. Next, determine the relative luminance of the darker color.

For this example, the luminance is found to be .125.

3. Finally, calculate the contrast ratio.

Using the formula, the contrast ratio is found to be (.215+.05) / (.125 + .05 ) = .220/.130 = 1.692 : 1.