APCA Contrast Checker
Advanced Perceptual Contrast Algorithm
Okay,
We are what we repeatedly do; excellence, then, is not an act but a habit.
Aristotle
What is APCA (WCAG 3.0 Draft)?
APCA (Advanced Perceptual Contrast Algorithm) is the proposed replacement for WCAG 2.x contrast formulas, designed for WCAG 3.0. It calculates contrast based on human perception rather than raw luminance ratios, producing more accurate accessibility guidance.
The key innovation: APCA considers that dark text on light backgrounds and light text on dark backgrounds don't perceive equally. A 7:1 WCAG ratio for white-on-dark may look similar to 4.5:1 dark-on-white—something WCAG 2.x doesn't account for.
Why APCA (WCAG 3.0 Draft) Matters
APCA better represents how humans actually see contrast. Colors that fail WCAG but pass APCA are often perfectly readable. Colors that pass WCAG but fail APCA may genuinely be hard to read.
For design teams frustrated by WCAG rejecting obviously-readable combinations, APCA offers relief. It validates what designers intuitively understand while still protecting accessibility.
APCA (WCAG 3.0 Draft) Requirements
APCA uses Lightness Contrast (Lc) values instead of ratios:
**Body text (16px+):** Lc 60 minimum **Subheads and large text:** Lc 45 minimum **Large headlines:** Lc 30 minimum
Positive Lc values indicate dark-on-light; negative values indicate light-on-dark. Both meet the same thresholds.
How to Pass APCA (WCAG 3.0 Draft)
- Use APCA for modern, perception-accurate testing
- Don't abandon WCAG 2.x yet—it's still the legal standard
- Test critical text at multiple sizes
- Consider both WCAG and APCA during development
Pro Tip
APCA is still a draft standard. Use it to inform design decisions, but ensure WCAG 2.x AA compliance for legal protection.
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