About

In digital product design, accessibility is a fundamental requirement, not an optional enhancement. The Web Content Accessibility Guidelines (WCAG) 2.1 mandate specific contrast ratios between text and background colors to ensure content remains legible for users with visual impairments, including low vision and color blindness. Failure to meet these standards can result in poor user experience, reduced conversion rates, and legal liability under regulations like the ADA (Americans with Disabilities Act) and Section 508.

This tool goes beyond simple pass/fail metrics. It simulates how your color palette appears on actual user interface components (buttons, cards, inputs) and visualizes the experience through the lens of various vision deficiencies (Protanopia, Deuteranopia). By calculating relative luminance using the precise W3C algorithms, it provides mathematical certainty for your design system's compliance. We also include an intelligent "Smart Fix" algorithm that mathematically determines the nearest compliant color shade, saving hours of manual trial and error.

Formulas

The WCAG 2.1 contrast ratio is calculated using relative luminance (L). The formula compares the luminance of the lighter color (L₁) against the darker color (L₂):

Ratio = L₁ + 0.05L₂ + 0.05

To find luminance, RGB values (0-255) are first linearized to remove gamma correction. For a color component C (where C is R, G, or B divided by 255):

C_lin =

{

C12.92 if C ≤ 0.03928C + 0.0551.055^2.4 otherwise

The total relative luminance is a weighted sum representing human eye sensitivity:

L = 0.2126R_lin + 0.7152G_lin + 0.0722B_lin

Reference Data

Compliance Level	Min Ratio	Context & Use Case	Visual Impact
WCAG AA (Regular)	4.5:1	Body text (size < 18pt). Standard for nearly all web text.	Readable for users with 20/40 vision loss.
WCAG AA (Large)	3.0:1	Headlines ≥ 18pt (24px) or Bold ≥ 14pt (18.5px).	Acceptable for large UI elements.
WCAG AA (UI)	3.0:1	Input borders, icons, focus states, and charts.	Ensures functional elements are visible.
WCAG AAA (Regular)	7.0:1	High-priority text. Required for government/public sector.	Readable for users with 20/80 vision loss.
WCAG AAA (Large)	4.5:1	Large headings in strict compliance environments.	Maximum accessibility standard.
Incidental	N/A	Disabled buttons, decorative logos, invisible elements.	No contrast requirement.
Pure Black/White	21.0:1	Maximum theoretical contrast.	High visibility, potentially harsh on eyes.
Low Contrast	< 3.0:1	Fails all text standards.	Invisible to many users; legally risky.

Frequently Asked Questions

Large text (defined as 18pt regular or 14pt bold) is easier for the eye to process because the strokes are wider. WCAG permits a lower contrast ratio (3.0:1) for these elements compared to body text (4.5:1), as the physical size compensates for the lower luminance difference.

Level AA is the industry standard for most commercial websites and is legally required by many jurisdictions. It balances accessibility with design flexibility. Level AAA is a stricter standard (7.0:1 ratio) intended for specialized content or audiences with significant visual impairments. While AAA is ideal, it significantly limits the available color palette.

The simulator uses a color matrix transformation (LMS color space) to mathematically approximate how cones in the human eye perceive light when specific photopigments are missing or defective. This allows designers with normal vision to "see" the interface as a user with Protanopia (red-blind) or Deuteranopia (green-blind) would, highlighting potential usability issues.

APCA (Advanced Perceptual Contrast Algorithm) is a newer, more sophisticated method proposed for WCAG 3.0. It accounts for font weight, size, and context better than the current method. However, WCAG 2.1 (the formula used here) remains the current legal standard. Until WCAG 3.0 is officially ratified, adherence to the 2.1 ratios is required for compliance.

Orange and yellow are notoriously difficult colors in accessibility. They have high intrinsic luminance, meaning they are mathematically close to white. To pass AA (3.0:1) on white, an orange must be quite dark (often brownish). Alternatively, use black text on the orange button, which almost always passes.