🔬 APCA Contrast Checker (WCAG 3)
Measure text/background contrast the WCAG 3 way: APCA reports a signed Lc value (0–±106) that accounts for polarity and maps to a minimum readable font size.
The quick brown fox jumps
over the lazy dog — 16px body sample
APCA lightness contrast
Lc 77.2
dark text on light bg
WCAG 2 ratio (for comparison)
5.45:1
AA normal ✓
Min size — regular (400)
≈ 14px+ body text
Min size — bold (700)
≈ 14px+ body text
APCA-W3 version 0.1.9 (the version referenced by the WCAG 3 working draft). Lc is polarity-aware and maps to a minimum font size. 🔒 Computed in your browser.
How the apca contrast checker (wcag 3) works
APCA (Accessible Perceptual Contrast Algorithm) estimates the perceived lightness contrast between text and background. The tool computes screen luminance for each color with the APCA exponents, applies the soft black-clamp, and derives Lc — positive for dark-on-light, negative for light-on-dark — then looks up the minimum font size and weight that Lc supports. It shows the WCAG 2 ratio beside it so you can compare the two methods.
APCA is the contrast method in the draft WCAG 3 and behaves very differently from WCAG 2: it is polarity-aware (dark-on-light vs light-on-dark are not symmetric) and ties contrast to font size. This checker is pinned to APCA-W3 version 0.1.9 — stated on-page because APCA is still versioned.
Frequently asked questions
What is APCA?
APCA (Accessible Perceptual Contrast Algorithm) is the contrast method proposed for WCAG 3. Instead of a ratio, it reports Lc — a lightness-contrast value from about 0 to ±106 — that better matches how humans perceive text readability, factoring in whether text is dark-on-light or light-on-dark.
What Lc value do I need?
As a guide: Lc 90+ for fine print and body text, Lc 75 for larger body text, Lc 60 for large/bold headings, Lc 45 for large display text, and Lc 30 as a non-text minimum. The tool shows the minimum font size each Lc supports.
How is APCA different from WCAG 2 contrast?
WCAG 2 uses a symmetric ratio (1–21) that ignores polarity and font size. APCA is polarity-aware and size-linked, so some pairs that pass WCAG 2 can be weak in APCA and vice-versa. This tool shows both numbers side by side.
Which APCA version does this use?
It is pinned to APCA-W3 0.1.9, the version referenced by the current WCAG 3 working draft. APCA has changed across releases, so the version is stated on the page for reproducibility.
Should I use APCA or WCAG 2 today?
WCAG 2 is the standard currently referenced by law (EAA, ADA, Section 508), so use it for compliance. APCA is worth checking as a forward-looking, often more realistic readability signal — many teams report both.