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WCAG Relative Contrast Ratio Calculator
Contrast ratio from two relative luminances.
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Contrast ratio
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Contrast ratio from two relative luminances.
WCAG Relative Contrast Ratio Estimator
Enter your numbers below for an instant estimate.
0
💡 Tip: Ratio = (L1 + 0.05) / (L2 + 0.05)
How It Works
Key concepts behind this calculator
1
Enter Values
Fill in each field with your own numbers.
2
Calculate
Results update as you change the inputs.
3
Review
Read the breakdown and the explanation.
4
Adjust
Change values to compare scenarios.
Quick Reference Guide
WCAG Quick Guide
Typical values for reference.
| Lighter luminance (0-1) | Darker luminance (0-1) | Spare | Contrast ratio |
|---|---|---|---|
| 1 | 0.2 | 0 | 4.20 : 1 |
| 1 | 0.05 | 0 | 10.5 : 1 |
| 0.4 | 0.3 | 0 | 1.29 : 1 |
| 0.9 | 0.1 | 0 | 6.33 : 1 |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Common Questions
WCAG Relative Contrast Calculator FAQ
Answers to common questions about this calculator.
It uses the formula shown with your inputs. Real conditions vary, so treat it as a guide.
Ratio = (L1 + 0.05) / (L2 + 0.05)
It is an estimate based on the inputs you enter. Check real quotes, labels or official guidance for important decisions.
Yes. Replace each input with your own figures and the result updates instantly.