By ColorUI Team7 min read
APCA vs WCAG 2.1 Contrast: Which Should You Use in 2025?
WCAG 2.1 contrast ratios are reliable but blunt. APCA is the modern perceptual alternative shipping with WCAG 3. Here is when to pick which.
The headline
WCAG 2.1 uses a single contrast ratio (1:1 to 21:1) computed from luminance. APCA returns an Lc value (-108 to +106) that takes polarity, font weight and font size into account. Both are valid; they answer different questions.
Where WCAG 2.1 is great
- Required by law in most jurisdictions (ADA, EAA, AODA).
- One number, easy to communicate.
- Universally tooled - every checker on the planet supports it.
Where WCAG 2.1 falls short
- Treats white-on-black and black-on-white identically, even though humans see them very differently.
- Ignores font weight - 200-weight at 4.5:1 is still a "pass" but is barely readable.
- Penalizes mid-tone designs that are objectively legible.
What APCA changes
APCA models how the human eye actually perceives contrast: it weighs background polarity, applies a non-linear lightness curve, and ties thresholds to font weight x size. Apple, Adobe and many design systems already ship with APCA-aware tokens.
How to use both
- Compliance baseline. Pass WCAG 2.1 AA on every text token.
- Design judgement. Use APCA Lc to tune body text vs headlines vs UI states. A heading at -75 Lc is rich; body at -90 Lc is comfortable.
- Document both. When you propose a token color, ship it with the WCAG ratio AND the APCA Lc.
Check both in one screen at our Contrast Checker, or fix failing pairs automatically in Fix A11y.