Contrast Ratio Calculator

For optimal readability, WCAG guidelines recommend a minimum contrast ratio of 4.5:1 for normal text and 3:1 for large text. For enhanced accessibility (WCAG AAA level), aim for 7:1 for normal text and 4.5:1 for large text. Higher contrast (around 10:1 or greater) is beneficial for users with severe visual impairments or reading in challenging conditions.

Contrast ratio is calculated using the relative luminance of the text and background colors. The formula is (L1 + 0.05) / (L2 + 0.05), where L1 is the relative luminance of the lighter color and L2 is the relative luminance of the darker color. Luminance is calculated from the RGB values using a formula that accounts for human perception of different color channels.

The Web Content Accessibility Guidelines (WCAG) define these contrast requirements:

• WCAG AA level: Minimum 4.5:1 ratio for normal text (under 18pt) and 3:1 for large text (18pt or 14pt bold and larger)
• WCAG AAA level: Minimum 7:1 ratio for normal text and 4.5:1 for large text

These standards ensure content is readable by people with visual impairments, including color vision deficiencies.

Sufficient contrast between text and background is essential for readability and accessibility. Many users, including those with low vision, color blindness, or cognitive disabilities, struggle to read text with poor contrast. Additionally, environmental factors like glare, poor lighting, or viewing screens outdoors can make low-contrast text virtually unreadable for anyone. Proper contrast ensures your content remains accessible across different devices, environmental conditions, and to users with various visual abilities.

The highest contrast combinations typically include:

• Black text on white background (21:1 ratio)
• White text on black background (21:1 ratio)
• Dark blue text on white background (approximately 16:1 ratio)
• Yellow text on black background (approximately 19:1 ratio)

However, extremely high contrast can cause eye strain during extended reading. For lengthy content, slightly softened contrast (like dark gray on white) while still maintaining WCAG compliance can be more comfortable for extended reading.

Yes, contrast requirements extend beyond text. WCAG 2.1 requires a minimum 3:1 contrast ratio for graphical objects (like icons) and UI components that convey information or require user interaction. This includes form controls, focus indicators, and essential graphics. Decorative images don't have specific contrast requirements, but informational images should have sufficient contrast to be perceived by users with low vision or color vision deficiencies.

The fundamental contrast requirements remain the same for both dark and light modes, but there are some practical considerations. In dark mode (light text on dark backgrounds), some users may need higher contrast than the minimum requirements due to the "halation effect," where light text can appear to bleed into dark backgrounds for some users with astigmatism or other visual conditions. It's recommended to exceed minimum contrast requirements for dark mode interfaces by using pure white text (#FFFFFF) on very dark backgrounds (darker than #121212).

No, using color as the only visual means of conveying information is not accessible. Even with sufficient color contrast, approximately 4.5% of the population has some form of color vision deficiency. WCAG guidelines (Success Criterion 1.4.1) require that color not be used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. Always supplement color with text labels, patterns, shapes, or other visual indicators.