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APCA Contrast Calculator — The New WCAG 3 Contrast Algorithm

Calculate contrast using APCA (Advanced Perceptual Contrast Algorithm) — a genuinely different, more perceptually accurate contrast model than the WCAG 2.x contrast ratio formula, currently proposed as the basis for WCAG 3's contrast requirements, since the older ratio-based formula is known to misjudge contrast for certain color combinations, especially with light text on dark backgrounds.

How to use APCA Contrast Pro

1. Enter foreground and background colors.
2. Read the calculated APCA contrast value (Lc).
3. Compare against APCA's recommended thresholds for your text size and weight.

Frequently asked questions

How is APCA different from the standard WCAG 2 contrast ratio?

WCAG 2 uses a single ratio formula for all color pairs; APCA uses perceptually-based math that accounts for text size, weight and polarity (light-on-dark vs dark-on-light), which the older ratio formula is known to get measurably wrong in some cases.

Should I use APCA or WCAG 2 contrast ratio today?

WCAG 2.x ratio is still the current formal accessibility standard most audits check against; APCA is the direction WCAG 3 is heading and worth understanding early, but is not yet the enforced legal/compliance standard.

What does the Lc value mean?

APCA outputs a signed Lc (Lightness Contrast) value rather than a simple ratio — the sign indicates polarity and the magnitude indicates contrast strength against size/weight-specific recommended thresholds.

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