Date Add / Subtract Calculator
About APCA Contrast Calculator
The Advanced Perceptual Contrast Algorithm (APCA / WCAG 3.0 Bronze/Silver/Gold) Calculator computes lightness contrast ($L^c$) based on spatial frequency, font weight, font size, and human visual perception models.
How to Use APCA Contrast Calculator
Step 1
Select Text Color and Background Color.
Step 2
Enter your desired font size and font weight.
Step 3
Review computed $L^c$ score and readable use case recommendations (Body, Large Title, Placeholder).
Step 4
Click "Copy APCA Report".
Practical Use Cases for APCA Contrast Calculator
WCAG 3.0 Readiness & Modern Design System Readability Engineering
Evaluate UI color combinations using perceptual contrast ($L^c$) rather than outdated mathematical ratios for superior dark mode legibility.
Font Weight & Size Pairing Optimization for Muted UI Elements
Determine the exact minimum font weight (e.g. 400 vs. 600) required for subtle secondary text on light/dark backgrounds under APCA guidelines.
Input & Output Examples
Testing Black `#111827` on White `#FFFFFF` with 16px Regular Font
Text Color: `#111827`, Background: `#FFFFFF`, Font: `16px / 400 Regular`
APCA Score ($L^c$): `+104.2` | Minimum Required: `Lc 60` | WCAG 3.0 Status: `Passes for all body text, small print, and headings`
Key Features & Performance
- ✓Official APCA-W3 Math Engine: implements the official Accessible Perceptual Contrast Algorithm ($L^c$ $-108$ to $+108$).
- ✓Dynamic Font Lookup Table: suggests minimum compliant font size and font weight for any calculated $L^c$ score.
- ✓Polarity Detection: distinguishes positive polarity (dark text on light background) from negative polarity (light text on dark background).
- ✓100% Client-Side memory execution.
- ✓1-Click Copy APCA compliance report.
Key Terminology & Definitions
APCA ($L^c$ Lightness Contrast)
A color vision model proposed for WCAG 3.0 that predicts human perceptual contrast based on spatial frequency, font size, and modern display characteristics.
Polarity Effect
The phenomenon where human eyes perceive contrast differently for dark text on light backgrounds (positive) versus light text on dark backgrounds (negative).