Font Accessibility Engineering: WCAG Standards for Readability and Usability

Making a font usable and accessible is critical to the success of any digital project. Readability is a function that goes beyond mere aesthetics; it requires an engineering methodology that ensures easy content interaction for a wide range of users, including those with visual impairments and reading difficulties.

1. Vertical Metrics & Optical Adjustments

These factors determine readability at the character and line level:

• Font Size and X-Height: Body text should be at least 16 pixels (or equivalent relative units) according to WCAG recommendations. Fonts with a high X-Height are generally considered more legible.
• Font Weight and Clarity: Weights between Regular and SemiBold are preferred for most paragraph texts. Very thin weights collapse on bright screens.
• Line Height / Leading: The optimal Line Height should range between 1.4 to 1.6 times the font size. This ensures sufficient visual separation for easy line tracking.

2. Spacing and Differentiation

The space surrounding the characters is key to clarity:

• Kerning & Tracking: The spacing between characters (Tracking) must be set to prevent adjacent letters from running together. For cognitive disabilities like Dyslexia, slightly increased spacing (Loose Tracking) is recommended for better differentiation.
• Clarity of Form (Legibility): Choose a font with clear differences between similar characters (e.g., capital I, lowercase l, and the number 1).
• Line Length / Measure: The best line length for paragraph text ranges from 50 to 75 characters (including spaces) to facilitate reading tracking.

3. Color and Contrast Ratios

Contrast is a fundamental factor for accessibility compliance:

• Contrast Ratios (WCAG AA/AAA): Standard body text must achieve a contrast ratio of at least 4.5:1 (for WCAG AA level).
• Avoid Relying on Color: Color should never be the sole means of conveying information (e.g., do not rely only on red to indicate an "error").

4. Systemic Use & Font Compatibility

• Typeface Selection: Simple, geometric Sans Serif fonts are the preferred choice for screen reading due to their clarity. For Arabic scripts, modern, simplified Naskh typefaces are best for long-form reading.
• Avoid Over-Use: It is recommended to use a maximum of two or three typefaces within a single project to maintain visual consistency and reduce page load time.
• Cross-Platform Testing: The font (exported as WOFF/WOFF2 for the web) must be tested across different browsers, operating systems, and devices to ensure consistent rendering.

5. Integrating Assistive Technology

The font must be designed to work harmoniously with accessibility tools:

• Screen Readers: The page structure must be compatible, and the font text must be correctly encoded with Unicode for proper reading by the software.
• Page Zoom: Font metrics should be relative (using rem or em) so users can zoom the text up to **200%** (WCAG requirement) without breaking the page layout.

Conclusion: A user-friendly font is one that respects the reader. The key lies in applying engineering standards (like testing Kerning and X-Height) and adhering to global accessibility guidelines (WCAG) to ensure that the visual design serves its primary goal: clear and inclusive communication.