By ColorUI Team5 min read
WCAG Contrast, Explained Without the Jargon
What 4.5:1 actually means, why 3:1 is enough for big text, and how the new APCA algorithm changes everything.
The ratio
Contrast ratio is a number between 1:1 (no contrast - invisible) and 21:1 (pure black on pure white). It compares the relative luminance of two colors.
The thresholds
- 3:1 - minimum for large text (18pt+ or 14pt bold) and graphical elements (AA Large).
- 4.5:1 - minimum for body text (AA).
- 7:1 - enhanced contrast (AAA).
What about APCA?
The Accessible Perceptual Contrast Algorithm, used in WCAG 3 drafts, models how humans actually perceive contrast against different backgrounds. It is more accurate but not yet a hard requirement.
Test your colors instantly in the Contrast Checker.