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Is that text actually readable?

Pick a text color and a background, and this returns the true WCAG contrast ratio — the same math accessibility audits use — with AA and AAA pass or fail.

Large text sampleNormal body text sample — the quick brown fox jumps over the lazy dog.
CONTRAST RATIO—
Normal text
AA (4.5:1)—
AAA (7:1)—
Large text (18pt / 14pt bold)
AA (3:1)—
AAA (4.5:1)—

How this is calculated

This is the standard WCAG 2.x formula, not an approximation. Each channel is normalized to the 0–1 range and linearized (values at or below 0.03928 divide by 12.92; the rest use((c + 0.055) / 1.055) ^ 2.4). Relative luminance isL = 0.2126R + 0.7152G + 0.0722B, and the contrast ratio is(L_lighter + 0.05) / (L_darker + 0.05), giving a value from 1:1 to 21:1.

The thresholds: normal text needs 4.5:1 for AA and 7:1 for AAA; large text (18pt, or 14pt bold) needs 3:1 and 4.5:1. Contrast is only one part of readable design — aUI/UX designer weighs it against type size, spacing, and hierarchy. If you're building the site yourself, pair this with theprint bleed calculator for any physical collateral.