WCAG Contrast Checker — FAQ
7 common questions about contrast ratios, AA/AAA, and how the numbers work.
Frequently asked questions (7)
What contrast ratio passes WCAG AA?
Level AA (SC 1.4.3) requires a contrast ratio of at least 4.5:1 for normal text and at least 3:1 for large text. For user-interface components and meaningful graphics, SC 1.4.11 requires at least 3:1. A combination passes when its measured ratio is greater than or equal to that threshold.
What contrast ratio is needed for AAA?
Level AAA (SC 1.4.6) is stricter: at least 7:1 for normal text and 4.5:1 for large text. There is no AAA level for non-text (UI) contrast, so 3:1 remains the bar there. AAA is a great target for long-form body copy, though AA is the level most policies require.
What counts as "large text"?
Large text is at least 18pt (about 24px) at a regular weight, or at least 14pt (about 18.66px) when bold. Large text may use the relaxed 3:1 (AA) or 4.5:1 (AAA) thresholds. Anything smaller is normal text and must meet 4.5:1 (AA) or 7:1 (AAA).
How is the contrast ratio calculated?
Each sRGB channel is normalized to 0–1 and linearized (c/12.92 when the value is at or below 0.03928, otherwise ((c+0.055)/1.055)^2.4). Those linear channels combine into relative luminance L = 0.2126R + 0.7152G + 0.0722B, and the ratio is (L1 + 0.05) / (L2 + 0.05) with L1 the lighter color.
Why does gray #777777 fail on white but #767676 passes?
Contrast is very sensitive near the 4.5:1 threshold. Medium gray #777777 on white computes to about 4.48:1, just under the AA minimum, so it fails for normal text. One shade darker, #767676, reaches about 4.54:1 and passes. This is why a checker with exact math beats eyeballing it.
Does transparency or opacity affect the result?
This tool ignores alpha and treats every color as fully opaque. Real semi-transparent text blends with whatever is behind it, changing the effective color and contrast. Flatten the color against its actual backdrop first (compute the composited RGB), then check that resulting solid color here.
Is this the same as APCA / WCAG 3?
No. This checker uses the WCAG 2.x contrast-ratio algorithm, which is the current W3C Recommendation. APCA (Advanced Perceptual Contrast Algorithm) is part of the in-progress WCAG 3 draft and is not yet normative, so results and thresholds differ. Use WCAG 2.x for conformance today.