WCAG Contrast Checker
Calculate contrast from foreground and background relative luminance and compare AA/AAA thresholds for normal and large text. This checks one colour relationship rather than certifying an entire page.
- Runs in your browser
- Nothing is uploaded
- No signup; device limits apply
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How to use this tool
Enter supported hexadecimal colours. Text over transparency, images or gradients needs the actual composited background, so a single uncomposited colour pair may not describe the visible result.
Results and examples
Black on white has a 21:1 ratio. AA requires 4.5:1 for normal text and 3:1 for qualifying large text; a ratio of 4.499 must not be rounded into a pass.
Limitations
- Large-text thresholds require the specified size and weight conditions, not a subjective impression.
- Keyboard operation, labels and semantic structure need separate accessibility checks.
Fields
| Field | Guidance and constraints |
|---|---|
| Foreground (text) HEX | Check the unit and format displayed beside this field. |
| Background HEX | Check the unit and format displayed beside this field. |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Sources
Frequently asked questions
What is black-on-white contrast?
Black on white has a 21:1 ratio. AA requires 4.5:1 for normal text and 3:1 for qualifying large text; a ratio of 4.499 must not be rounded into a pass.
Does a pass certify the whole page?
Large-text thresholds require the specified size and weight conditions, not a subjective impression. Keyboard operation, labels and semantic structure need separate accessibility checks.
