Text needs a contrast ratio of at least 7:1 against its background. Large text - 24px or 18.5px bold and above - can drop to 4.5:1.

This is Level AAA. It's the stricter version of 1.4.3 Contrast (Minimum), which asks for 4.5:1 at Level AA.

AA vs AAA

Most accessibility legislation references Level AA. That's where 4.5:1 lives. AAA isn't legally required in most places, and the W3C says it's not recommended as a blanket policy for entire sites because it's not always possible for all content.

But it's useful as a target for specific parts of your design. If you can hit 7:1 for body text, you're making your content readable for people with more significant vision loss - not just people who need reading glasses.

Where the numbers come from

Same research as 4.5:1, extended further. ISO 9241-3 set 3:1 for normal vision. For 20/40 acuity you multiply by 1.5 to get 4.5:1 (AA). For 20/80 acuity - roughly the threshold for legal blindness - the contrast sensitivity loss is greater, and the same scaling logic gives you 7:1.

The large text exception at AAA drops to 4.5:1 (the same ratio as AA for normal text). Bigger characters, thicker strokes, easier to perceive.

When to aim for it

You don't need 7:1 everywhere. But it's worth targeting for:

• Body text and long-form content. If people spend time reading - docs, articles, terms - higher contrast reduces fatigue.

• Critical information. Error messages, warnings, legal text, anything where the cost of someone missing it is high.

• Older audiences. If your users include people over 50, contrast sensitivity loss is common enough that 4.5:1 can fall short. Government services, healthcare, financial tools.

For headings, navigation, and shorter text, AA is usually fine. Focus AAA effort where people actually read.

Things to watch for

"High contrast" doesn't mean "black and white." Plenty of colour combinations pass 7:1. Dark navy on white, dark grey on cream, dark green on pale grey. You don't have to flatten your palette to hit AAA.

Large text still gets breathing room. At AAA, large text (24px or 18.5px bold) only needs 4.5:1 - the same as AA for normal text. Your headings don't need to be as tightly controlled as your body copy.

Don't treat it as pass/fail for the whole design. AAA is better understood as a quality target for the parts of your design that matter most for readability. Test your body copy against 7:1. Test your headings against 4.5:1. Meet AA for everything else.

In Perception

Perception tests against both AA and AAA in every scan. You don't need to run separate checks or change any settings.

Each result shows whether it passes AA (4.5:1), AAA (7:1), or both. Large text is detected automatically and tested against the lower thresholds. Filter by pass/fail at each level to focus on what needs attention.

Related

• 1.4.3 Contrast (Minimum) - The AA version. 4.5:1 for normal text, 3:1 for large.

• 1.4.11 Non-text Contrast - 3:1 for icons, input borders, focus indicators, and other non-text elements.

• Text size - Why font size affects readability and when Perception flags small text.