Meet the enhanced 7:1 contrast ratio
Seven to one, measured between the text and whatever sits behind it. G17 is the enhanced contrast technique, and W3C files it as sufficient for the enhanced contrast rule, which is Level AAA. The Level AA minimum is a different number, 4.5:1, and Level AA is what accessibility law generally points at. So treat G17 as a target you choose rather than an obligation you carry. Large text gets a lower bar at both levels, and at the enhanced level it is 4.5:1 rather than the 3:1 that applies at AA, which is the detail teams aiming high miss most often. Where the background is a photograph or a gradient, the measurement runs against the part directly behind the letters, and shading that area is a legitimate way to hold the ratio.
How we find it in an audit
Contrast is arithmetic, so a tool measures it and the number is not open to opinion. We sample every text and background pairing in the design system rather than every paragraph on every page, because a design system produces a finite set of pairings and a site produces an endless one. Text over images gets measured behind the letters instead. Where a client is aiming at the enhanced level, the report says which pairings clear 7:1, which clear 4.5:1 and which clear neither, so the work can be planned rather than guessed at.
How affected users experience it
Low-vision readers do not meet contrast as a pass or a fail. They meet it as effort. Text at the AA minimum is legible and tiring, and an hour of it is an hour of squinting. Pushing to 7:1 is what turns readable into comfortable, and it pays out for everyone else too, on a phone in sunlight or on a cheap monitor with the brightness set wrong. Nobody has ever complained that the text was too easy to read.
Passes vs. fails
Passes
#595959 on white measures 7:1, which clears the enhanced level with room to spare for aging eyes.
Fails
Body text at #767676 on white passes AA at 4.5:1 and still takes real work for low-vision readers.
How this gets tested
The W3C publishes test rules that define what a checker looks for here.
- Text has enhanced contrastA tool can check this
- Text has minimum contrastA tool can check this
Other ways to satisfy this rule
7 guides on this site are filed under 1.4.6 Contrast (Enhanced). W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
- G18sufficientMeet the 4.5:1 contrast ratio for text
- G148sufficientLeave text colors default, or set both
- G174sufficientOffer a working switch to high-contrast view
- G156advisoryKeep text recolorable by the user's browser
- F24failureNever set text color without its background
- F83failureDo not set text over a low-contrast background image
This guide is our interpretation of W3C technique G17: Ensuring that a contrast ratio of at least 7:1 exists between text (and images of text) and background behind the text. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.