What is an acceptable APCA Lc score for body text?

Lc 75 is recommended for primary body text, while Lc 60 is acceptable for secondary text and larger headings.

What does a negative Lc score mean?

A negative Lc indicates dark mode (light text on dark background), which humans perceive with different neural spatial properties.

Is APCA currently a legal accessibility requirement?

WCAG 2.1 AA remains the current legal standard in most jurisdictions, with APCA serving as the forward-looking best practice.

Accessibility & A11y Tools• WCAG 3 Beta

APCA Contrast Calculator (WCAG 3 Readability)

APCA (Advanced Perceptual Contrast Algorithm) is the candidate contrast method for WCAG 3. It accounts for spatial frequency, font size, weight, and human photoreceptor non-linearities.

Computed entirely on client device. Zero network telemetry.

APCA Parameters

Text Color

Background Color

APCA Lightness Contrast (Lc)

Lc 95(Dark on Light)

Lc 90+: Preferred for fluent body reading

Lc 75+: Minimum for 16px body text

Lc 60+: Minimum for 24px bold headlines

Lc 45+: Minimum for large icons and inactive elements

Sponsored PlacementGoogle AdSense Integration Ready

How to Use APCA Contrast Calculator

Input Colors

Provide foreground text color and background surface color.

Select Font Size & Weight

Specify target font size in pixels and font weight (e.g., 400 regular or 700 bold).

Evaluate Lc Score

Review the calculated Lc contrast value and minimum recommended text size.

About APCA Contrast Calculator

APCA calculates perceptual contrast using power-law gamma compression (approx 0.56 / 0.62) tailored to human foveal cone response, producing an Lc score that varies based on polarity.

Supported Formats

HEXRGB

Operational Limits

•APCA is a public working draft algorithm under consideration for WCAG 3.0.

Key Features

Candidate WCAG 3 APCA 0.98G algorithm implementation
Calculates signed Lightness Contrast (Lc) from -108 to +108
Dynamic font size and weight compliance lookup table
Light mode and dark mode polarity awareness
Direct comparison with legacy WCAG 2.1 contrast ratios

Frequently Asked Questions

WCAG 2.1 uses a simple mathematical ratio that fails on dark mode and thin fonts. APCA models actual human optical perception, font weight, and polarity.

Related Tools

WCAG Color Contrast Checker

Calculate foreground and background color contrast ratios in real time with WCAG 2.1 Level AA and AAA pass/fail compliance indicators.

Accessibility & A11y ToolsOpen Tool

3:1 Threshold Local

Large Text Contrast Checker

Specialized WCAG validator for large typography (18pt/24px normal or 14pt/18.66px bold) requiring 3:1 minimum contrast.

Accessibility & A11y ToolsOpen Tool

SC 1.4.11 Local

UI Component Contrast Validator

Validate WCAG 2.1 Success Criterion 1.4.11 for non-text UI elements: form input borders, button outlines, icons, and focus rings.

Accessibility & A11y ToolsOpen Tool