AODA Colour
Contrast Checker
Check if your text and background colours meet WCAG 2.0 AA — required under Ontario's AODA for all websites.
Quick presets
Normal text — 16px (WCAG AA requires 4.5:1)
This is how body text appears to your visitors. Ontario's AODA requires all text to meet WCAG 2.0 Level AA minimum contrast.
Large text — 24px (WCAG AA requires 3.0:1)
14.63:1
Contrast ratio
AA — Normal text
Requires 4.5:1
AA — Large text
Requires 3:1
AAA — Normal text
Requires 7:1
AAA — Large text
Requires 4.5:1
Excellent — this combination passes all WCAG AA and AAA requirements.
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WCAG Colour Contrast & AODA — Frequently Asked Questions
Does AODA require specific colour contrast on my website?
Yes. Ontario Regulation 191/11 (the Integrated Accessibility Standards Regulation) requires all Ontario organizations with one or more employees to meet WCAG 2.0 Level AA for their websites. Colour contrast is a core WCAG criterion — Success Criterion 1.4.3 requires a minimum contrast ratio of 4.5:1 for normal text and 3.0:1 for large text (18pt or 14pt bold).
What is the WCAG contrast ratio requirement?
WCAG 2.0 Level AA (the Ontario AODA standard) has two contrast thresholds. Normal text — anything below 18pt regular weight or 14pt bold — must achieve a 4.5:1 ratio. Large text at or above those sizes only needs 3.0:1. WCAG AAA, the highest level, raises these to 7.0:1 and 4.5:1 respectively. AODA mandates AA, not AAA.
How is colour contrast ratio calculated?
The contrast ratio is calculated using the relative luminance of each colour. Each RGB channel is linearized (gamma-corrected), then combined as 0.2126R + 0.7152G + 0.0722B to get luminance. The ratio is (L1 + 0.05) / (L2 + 0.05) where L1 is the lighter colour. A ratio of 1:1 means identical colours; 21:1 is pure black on pure white — the maximum possible.
What counts as "large text" under WCAG?
WCAG defines large text as 18pt (24px) or larger for regular weight, or 14pt (approximately 18.67px) or larger for bold text. If your text is below these sizes, it must meet the 4.5:1 threshold. Most body text on websites is 14–16px regular weight, so it falls under the stricter 4.5:1 requirement.
My site fails contrast — how do I fix it?
The most reliable fix is to darken the text colour or lighten the background until the ratio passes. Small adjustments to lightness in HSL colour space are usually enough — a mid-grey (#888888 on white) gives only 3.5:1 but #767676 just barely passes at 4.54:1. Avoid relying on font weight alone; contrast ratio does not change with weight in WCAG 2.0. Tools like the AODACheck website scanner will flag every failing element on your pages, not just the ones you test manually.