Corner radius has quietly converged. The data on geometry says a lot about where design is right now.
Corner radius seems like the least interesting number on a page. It turned out to be one of the most revealing. When I averaged the radii across the library, the median landed at 10px — soft, but far from round. And a detail I did not expect: only about 12% of sites use pill-shaped buttons.
The radii split into three camps: sharp (0–4px), soft (5–15px) and round (16px and up). The soft camp is the largest by a clear margin. That middle ground — around 8 to 12px — reads as modern and friendly without tipping into the bubbly, consumer-app look that a large radius creates. It is a consensus precisely because it is safe in the good sense: it fits almost any brand.
If you followed component libraries and design Twitter, you would think every button became a pill in 2023. The measured web disagrees: roughly one site in eight. Fully rounded buttons carry a specific personality — approachable, soft, slightly playful — and most premium and technical brands do not want that read. They keep the button radius aligned with the rest of the system instead of making it a statement.
The specific number matters less than this: mixed radii is one of the fastest tells of unmanaged UI. A 6px card next to a 16px button next to a 4px input looks accidental because it is. The best sites pick one radius policy and enforce it everywhere. That discipline — not the exact value — is what separates a designed interface from a generated one.
I commit to a single radius early (usually 10–12px), write it as a token, and only break it for a deliberate reason. When prompting AI tools I state it once — "radius 10px everywhere" — because otherwise the model mixes values across components and the whole thing quietly falls apart. Geometry is a small decision that, left unmade, undermines everything above it. More on tokens in the design tokens guide.