Interactive targets must be at least 24 by 24 CSS pixels

The check also measures summary elements and elements with roles such as checkbox, tab and option, so listbox color swatches count. Disabled, hidden and zero-size targets are skipped, as are skip links parked off the page. A control’s visible <label> adds to its measured box.

A target is small when its width or height is below 24 CSS px, with 0.25 px allowed for sub-pixel layout. A small target still passes when:

• a 24 px circle centered on it reaches neither another target’s box nor the circle of another small target outside running text;
• it is an inline element, or an inline-block link, in a block that also holds text outside any target. A heading above a list of links does not count.

The check runs separately in each scanned viewport, by default desktop (1440 px) and mobile (390 px), so a target that shrinks only on phones is reported for mobile. It does not apply the equivalent, user agent control or essential exceptions; a person judges those.