What is Touch Target Size, and how large does WCAG require it to be?
Touch target size is how large the area is that actually registers a tap or click on a button, link or form control. It refers to the clickable area, not how big the icon looks: a 16-pixel icon wrapped in a 24-pixel clickable area counts as 24 pixels.
WCAG 2.2 added success criterion 2.5.8, Target Size (Minimum), at Level AA, requiring pointer targets of at least 24 by 24 CSS pixels. The stricter 2.5.5, Target Size (Enhanced), is Level AAA and sets the threshold at 44 by 44 pixels.
Why does this requirement exist?
Small targets are a barrier for many people: those with hand tremors or limited motor control mis-tap easily, and so do people using a phone one-handed or on the move. A mis-tap isn't just an inconvenience; if the neighboring target is something like Delete or Pay, it can cause a real error.
The thinking behind 2.5.8 is to set an achievable floor, 24 pixels, without forcing every element to be enlarged. Those who want a higher guarantee can aim for the 44 pixels of 2.5.5.
How do you tell in practice whether an element passes?
Measure the width and height of the clickable area; if both are at least 24 CSS pixels, it passes. A target smaller than that can still pass under an exception: spacing (at least 24 pixels of offset from every adjacent target), equivalent (another control on the same page that meets the criterion achieves the same function), inline (the target is inside a sentence or Block of text), user agent control (the browser determines the size and the author hasn't changed it), or essential (a particular presentation is essential or legally required).
The spacing check works like this: center a 24-pixel-diameter circle on each undersized target's bounding box, and those circles must not intersect another target or another undersized target's circle.
What does this mean for designers and people generating interfaces with AI?
Icon buttons in design files are the easiest place to slip: 16 pixels looks clean visually, but if the clickable area is also only 16 pixels and sits tight against other buttons, it fails both the size and the spacing tests. The fix is usually not to enlarge the icon but to enlarge the clickable area with padding or to widen the spacing.
When generating interfaces with AI tools, this check deserves a place on the acceptance list. A third-party review reported that some generated results fell short of basic accessibility requirements on color contrast and touch-target size (that review comes from a competitor's site, so verify it yourself). Writing "every interactive element has a clickable area of at least 24 by 24 pixels" into the prompt and measuring before delivery is cheaper than patching afterward.
W3C's explanation of the spacing exception is the clearest example: a small 16-pixel icon button, though under 24 pixels itself, meets 2.5.8 as long as a 24-pixel-diameter circle centered on it does not intersect neighboring buttons or other undersized targets' circles; if two 16-pixel buttons sit flush against each other, the circles overlap and they fail. A link inside a sentence is covered directly by the inline exception and isn't held to 24 pixels.
The upside is a measurable floor that reduces mis-taps, helping people with limited motor control as well as mobile users; the downside is that in dense interfaces (toolbars, table action rows) meeting size and spacing takes more room, forcing a trade-off with information density, and 24 pixels is only a minimum that doesn't guarantee a target is actually comfortable to hit.