無料コントラストチェッカー

WCAG AAでは通常テキスト4.5:1以上、大きなテキスト3:1以上です。AAAでは通常テキスト7:1以上です。

WCAG基準では、大きなテキストは18pt（24px）以上、または14pt（18.66px）以上の太字テキストです。

十分なコントラストにより、視覚障害のある方を含むすべてのユーザーがコンテンツを読めるようになります。また、多くの地域でアクセシビリティ基準の遵守が法的に要求されています。

コントラスト比は色覚障害の有無に関わらず計算されます。十分なコントラスト比があれば、色覚障害のユーザーにもテキストが読みやすくなります。

AAは最低推奨基準、AAAはより厳格な強化基準です。ほとんどのウェブサイトはAA準拠を目指すべきです。

WCAG AA is the standard referenced by most accessibility laws worldwide, including the ADA (US), EAA (EU), and EN 301 549 (Europe). For most websites and apps, AA compliance is both legally sufficient and provides good readability. AAA is recommended for government sites, healthcare, and education, but is not typically required by law.

You have several options: slightly adjust the shade of your brand color (often a small lightness change is enough), use your brand color for decorative elements only and a high-contrast color for text, increase font size to qualify for the large text threshold, or add a semi-transparent overlay behind text placed on colored backgrounds. Our tool suggests the nearest accessible color automatically.

Absolutely. The same WCAG contrast requirements apply regardless of the color scheme. In fact, dark mode introduces unique challenges: pure white (#FFFFFF) text on a very dark background can cause halation (a glowing effect) for users with astigmatism. A slightly off-white (#E0E0E0 to #F0F0F0) on a dark gray (#1A1A1A to #2D2D2D) often provides better readability while still meeting AA standards.

High contrast ratios help colorblind users significantly, but contrast alone is not sufficient. WCAG also requires that color is not the sole means of conveying information (1.4.1). For example, don't use only red/green to indicate error/success — add icons or text labels. The contrast ratio formula accounts for luminance, not hue, so it helps across all types of color blindness.

You can use browser DevTools (Chrome's Lighthouse audit includes contrast checks), browser extensions like axe or WAVE, or paste your exact HEX/RGB values into this tool. For comprehensive testing, use automated tools like Lighthouse for a full-page scan, then manually verify any flagged elements. Remember to test hover states, focus styles, and placeholder text — these are commonly missed.