To check text contrast, identify the text and background colors, calculate their relative luminance, and compare the resulting ratio with WCAG 2.2’s threshold: at least 4.5:1 for ordinary text or 3:1 for large-scale text at Level AA. Use the unrounded ratio, and assess meaningful controls and graphics separately under the non-text contrast criterion.
What WCAG contrast ratio should text meet?
WCAG 2.2 Success Criterion 1.4.3, a Level AA criterion, requires a contrast ratio of at least 4.5:1 for ordinary text and images of text. Large-scale text may use the lower minimum of 3:1. The thresholds apply to text against its background, not as a general pass/fail rule for every pair of colors. See the WCAG 2.2 standard and W3C’s explanation of Contrast (Minimum).
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When does the 3:1 large-text threshold apply?
W3C’s technique describes large text as at least 18 point when not bold, or at least 14 point when bold. If the text does not meet one of those size-and-weight definitions, use 4.5:1 for the AA minimum.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsWhat is the stricter AAA target?
WCAG Level AAA’s Contrast (Enhanced) criterion uses 7:1 for ordinary text and 4.5:1 for large text. These are stricter optional targets, not the Level AA baseline. The thresholds and large-text definitions are explained by W3C in its contrast guidance.
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How to check a text and background color pair
- Identify the colors actually behind and on the text. Start with the foreground text color and the background immediately behind it in the design or rendered page. Check the combinations users will encounter in normal presentation.
- Choose the applicable threshold. Use 3:1 only if the text qualifies as large-scale; otherwise use 4.5:1 for Level AA.
- Calculate the contrast ratio. Use the relative-luminance method below, or a digital contrast checker. A tool can do the arithmetic, but confirm that it is evaluating the real foreground and background colors used in the content.
- Compare the unrounded result. A value below the threshold fails even if a checker rounds its display to the threshold. W3C explicitly notes that 4.499:1 does not meet a 4.5:1 requirement.
- Repeat for other relevant combinations. Recheck after changing a color, background, border, or overlay, and assess applicable non-text elements separately.
How the WCAG contrast calculation works
The ratio is calculated from relative luminance, not by comparing RGB channel values directly or judging hue by eye. For each color, first convert its sRGB channels to linear values; then calculate luminance and compare the lighter color with the darker one. The ratio ranges from 1:1 to 21:1.
Convert each sRGB channel to a linear value
For each 8-bit channel value, divide by 255 to get a normalized value C. Apply this conversion:
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- If C ≤ 0.04045, use C / 12.92.
- If C > 0.04045, use ((C + 0.055) / 1.055)2.4.
Calculate luminance and the ratio
Using the linearized red, green, and blue values, calculate relative luminance:
L = 0.2126R + 0.7152G + 0.0722B
Call the higher luminance L1 and the lower luminance L2. The contrast ratio is:
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(L1 + 0.05) / (L2 + 0.05)
For example, a calculated result of 4.6:1 exceeds the 4.5:1 AA minimum for ordinary text; a result of 4.4:1 does not. Judge the underlying result rather than relying on rounded display values.
Check controls and graphics separately from text
Passing the text threshold does not establish that every meaningful visual element has sufficient contrast. WCAG 2.2 Success Criterion 1.4.11 addresses visual information needed to identify user-interface components and states, and graphical objects needed to understand content. It generally requires at least 3:1 contrast for that information against adjacent colors, subject to the criterion’s exceptions. Text remains covered by the text contrast criteria. See W3C’s explanation of Non-text Contrast.
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Some text is exempt from SC 1.4.3, including incidental text such as inactive user-interface components and decoration, as well as logos and brand names. These exceptions do not remove the need to check other meaningful information in the interface. W3C’s WCAG 2.2 standard defines the criterion and its exceptions.
What if text sits on a gradient, image, or pattern?
A single background color may not describe the contrast behind every letter when the background varies. Check the text against the portions of the background that appear immediately behind it, including the least favorable areas. W3C’s techniques give examples such as shading the text area or adding a suitable halo to maintain contrast; these are possible approaches, not mandatory implementations. See Technique G18 and Technique G145.
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What a contrast checker can and cannot tell you
A calculator or design-tool checker can automate the luminance math, making it useful for a first review. W3C’s Easy Checks likewise presents contrast as a practical early accessibility check and gives 4.5:1 as the default minimum for normal-size text. A ratio result alone does not confirm that the tool selected the correct rendered colors, that variable backgrounds were handled, or that applicable non-text information was assessed. Review the actual interface and all relevant color combinations as well as the number.
Contrast is one part of accessible color use. Color should not be the sole way information is conveyed; for example, a status should not be communicated only by making text red or green.
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