Colour Contrast Ratio Calculator (WCAG)
WCAG contrast ratio between text and background colours — the accessibility pass/fail every designer needs.
WCAG sets the legal-ish accessibility bar: 4.5:1 for normal text (AA), 3:1 for large text, 7:1 for AAA. Black on white is the maximum 21:1; the trap is mid-grey text on white, beloved of designers and unreadable for low-vision users — '#999 on white' fails at 2.85:1. Roughly 1 in 12 men has colour-vision deficiency, so contrast carries information colour alone can't.
Formula
For general information only — not medical advice, a diagnosis or a treatment plan. Consult a qualified healthcare professional before making health, diet, medication or exercise decisions.
WCAG contrast ratio between text and background colours — the accessibility pass/fail every designer needs. The Colour Contrast Ratio Calculator (WCAG) is a free, private contrast ratio calculator tool — every result computes instantly in your browser with no sign-up and no data upload.
About Colour Contrast Ratio Calculator (WCAG)
WCAG sets the legal-ish accessibility bar: 4.5:1 for normal text (AA), 3:1 for large text, 7:1 for AAA. It applies ratio = (L_lighter + 0.05) ÷ (L_darker + 0.05), L = relative luminance. Use the Colour Contrast Ratio Calculator (WCAG) to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use Colour Contrast Ratio Calculator (WCAG)
- 1Enter your details in the Colour Contrast Ratio Calculator (WCAG) input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use Colour Contrast Ratio Calculator (WCAG)?
- ✓Instant contrast ratio calculator result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (W3C WCAG 2.1 — contrast (minimum) success criteria)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Colour Contrast Ratio Calculator (WCAG) work?+
WCAG sets the legal-ish accessibility bar: 4.5:1 for normal text (AA), 3:1 for large text, 7:1 for AAA. The calculation uses the formula: ratio = (L_lighter + 0.05) ÷ (L_darker + 0.05), L = relative luminance. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Colour Contrast Ratio Calculator (WCAG) accurate, and what is it based on?+
The method is traceable to authoritative sources: W3C WCAG 2.1 — contrast (minimum) success criteria. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Colour Contrast Ratio Calculator (WCAG) free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This tool is for general information only and is not medical advice. Always consult a qualified healthcare professional before making health decisions.
What can I use the Colour Contrast Ratio Calculator (WCAG) for?+
It's commonly used for contrast ratio calculator, wcag contrast, color accessibility. WCAG contrast ratio between text and background colours — the accessibility pass/fail every designer needs.
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