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Color Contrast Checker

Calculate real-time luminance contrast ratios (1:1 to 21:1) between text foreground and background colors according to international WCAG 2.1 (Web Content Accessibility Guidelines) standards. Validates AA and AAA compliance for normal and large text with live interactive UI previews and lightness fine-tuning sliders.

Color Selection

Tweak Lightness

Foreground Lightness48%
Background Lightness100%

Adjust the sliders to quickly find the optimal lightness that satisfies accessibility compliance thresholds.

CONTRAST RATIO
9.14: 1

Excellent Contrast (Passes AAA)

AA Normal (Regular Text)
PASS
AA Large (Large Text)
PASS
AAA Normal (Regular Text)
PASS
AAA Large (Large Text)
PASS

Live Visual Preview

Web Accessibility & Inclusive Design

Clear visual contrast is the cornerstone of inclusive design for all users. This sample text illustrates real-time contrast at an 18px baseline.

UI Element

Text and UI component contrast updates instantaneously as colors are modified.

Client-Side Processing

Input HEX color values and relative luminance calculations are never transmitted to a cloud server. All computations happen in your local browser.

WCAG 2.1 Compliance Thresholds

Level AA requires a minimum ratio of 4.5:1 for regular text and 3.0:1 for large text (18pt+ or 14pt bold). Level AAA requires 7.0:1 for regular text and 4.5:1 for large text.

WCAG 2.1 Accessibility Color Guidelines

Relative Luminance Mathematics & WCAG Contrast Principles

Ensuring clear typographical contrast is vital for visually impaired users, people with color vision deficiencies, and anyone reading mobile screens under bright outdoor sunlight. The W3C’s WCAG 2.1 guidelines establish quantitative metrics for evaluating foreground-to-background contrast ratios.

ToolsYouWant Color Contrast Checker applies the W3C sRGB linearization formula and human eye spectral sensitivity weighting (Red: 21.26%, Green: 71.52%, Blue: 7.22%) to compute bit-accurate relative luminance values and contrast ratios.

Automatic WCAG 2.1 AA/AAA 4-Tier Validation

Instantly evaluates compliance across 4 categories: AA Normal, AA Large, AAA Normal, and AAA Large text.

Lightness Fine-Tuning Sliders

When contrast falls short, fine-tune lightness sliders to locate the nearest compliant color shade in seconds.

One-Click Color Swapping

Swap foreground and background colors with a single click to test dark mode and reversed UI palettes.

1. W3C Relative Luminance Formula

RGB channel values (0-255) are normalized to 0.0-1.0. If CsRGB≤0.03928C_{sRGB} \le 0.03928, Clinear=CsRGB/12.92C_{linear} = C_{sRGB} / 12.92. Otherwise, Clinear=((CsRGB+0.055)/1.055)2.4C_{linear} = ((C_{sRGB} + 0.055) / 1.055)^{2.4}.
Relative luminance LL is computed by multiplying linearized channels by spectral weighting: L=0.2126×R+0.7152×G+0.0722×BL = 0.2126 \times R + 0.7152 \times G + 0.0722 \times B.
The contrast ratio between lighter luminance L1L_1 and darker luminance L2L_2 is calculated as: Contrast Ratio=(L1+0.05)/(L2+0.05)\text{Contrast Ratio} = (L_1 + 0.05) / (L_2 + 0.05).

WCAG 2.1 Contrast Ratio Compliance Standards Table

Minimum contrast ratio thresholds defined by W3C across compliance tiers.

Accessibility LevelTypography CategoryMinimum Contrast RatioRecommended Application
Regular Text (< 18pt)
Large Text (18pt+ or 14pt Bold+)
Regular Text (< 18pt)
Large Text (18pt+ or 14pt Bold+)

2. Professional UI/UX Accessibility Design Tips

Pure black on pure white (#000000 on #FFFFFF) yields the maximum 21:1 ratio, but extreme contrast can cause visual fatigue for readers with dyslexia.
Using rich dark charcoals (such as #1E293B or #131B2E) maintains a comfortable, high-contrast 10:1 to 15:1 ratio that is easy on the eyes.
Always verify that placeholder text inside form inputs maintains at least a 4.5:1 ratio against the input background.

Frequently Asked Questions (FAQ)

Q.What is the exact definition of Large Text in WCAG?

W3C defines Large Text as 18pt (approximately 24px) or larger for normal weight, or 14pt (approximately 18.5px) or larger for bold weight typography.

Q.Do UI icons and form borders need to meet contrast ratios?

Yes. Under WCAG 2.1 Success Criterion 1.4.11 (Non-text Contrast), meaningful UI components like active icon toggles and input boundaries require a minimum 3.0:1 ratio.

Q.Is any color data sent to a remote server?

No. All calculations run locally in your browser via client-side JavaScript.

Guides for This Tool

Write-ups on how this tool is used in practice.

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Design & ColorsGuide
Color Contrast Checker
Color Contrast Checker 실전 가이드
#WCAG#Color Contrast

Understanding WCAG color contrast: A guide to web accessibility

Learn the mathematics behind WCAG color contrast, relative luminance formulas, and compliance thresholds for AA and AAA web accessibility standards.

September 30, 20264 min read

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