When is a rounded corner just right, when is too round or too squary ?
There are a bunch of rules in design such as the golden rectangle, the thirds, etc, is there one for rounded corners ?
I don’t think there is a rule, or even a suggestion about the size of rounded corners. That is purely aesthetic.
There are two key things to consider though:
- Consistency. Standardize the radius over a project. Avoid mixing and matching rounded corners of various sizes without a good reason.
- Concentricity. By all means, make sure your corners stay concentric if applicable. Our eyes expect to see concentric corners. Scaled corners just look odd.
See the How to compute the radii (radiuses) of corners for concentric rounded rects for a little more info.