Colour Contrast Checker
WCAG 2 contrast ratio for text on a background with AA / AAA verdicts by text size, APCA Lc as a second opinion, and the nearest text colour that passes.
The ratio, pass/fail for normal, large and UI at AA and AAA, the APCA Lc and what it allows, a preview, and a fixed text colour (same hue, lightness moved) that reaches AA and AAA.
Example: #777777 on white is 4.48 : 1 — fails AA for body text by a hair, passes for large text; #747474 fixes it (4.62). White on #ff8800 is 2.39 : 1 and APCA Lc 40: neither model allows text.
Two models,
one verdict you can act on.
How the WCAG ratio and APCA are computed, what the size rule is, and how the fix is found.
WCAG 2 ratio
Each colour is converted to relative luminance (sRGB channels linearised, weighted 0.2126 / 0.7152 / 0.0722); the ratio is (L₁ + 0.05) ÷ (L₂ + 0.05), lighter over darker, from 1 : 1 to 21 : 1. Normal text needs 4.5 (AA) or 7 (AAA); large text — 18 pt and up, or 14 pt and up when bold — needs 3 or 4.5; non-text UI parts and graphics need 3. The page converts your pixel size to points (× 0.75) to decide which rule applies.
APCA
APCA (the Accessible Perceptual Contrast Algorithm, candidate for WCAG 3) models perceived lightness contrast instead of a luminance ratio and is polarity-aware: it knows dark-on-light from light-on-dark. The Lc value shown comes from the public APCA-W3 0.1.9 formula; the size bands quoted (Lc 90, 75, 60, 45, 30) are its published guidance. It is shown as a second opinion — WCAG 2 remains the standard cited in law and audits.
The fix
When a level fails, the text colour is kept at the same hue and saturation and its HSL lightness is moved away from the background one step at a time until the target ratio is met; if that direction runs out, the other way is tried. It is the smallest change that passes, not necessarily the prettiest — use it as a starting point. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- WCAG 2.1 SC 1.4.3, 1.4.6, 1.4.11 (ratio (L₁ + 0.05)/(L₂ + 0.05), thresholds 4.5 / 7 / 3, large text ≥ 18 pt or 14 pt bold); APCA-W3 0.1.9 (Myndex) for Lc, shown for comparison
Last reviewed 22 September 2026. How results are checked: How we verify.