Radesign have an interesting post about what makes the perfect radius for buttons, icons, or anything with a border.
It’s a scientific approach to identifying something that people can often only ‘feel’ – the best look and feel for a design concept.
It’s summarised with this:
The next time you want to create nested rounded rectangles follow this to get the best results:
- Inner Radius = Outer Radius – Border Width
- If the inner radius = 0, fillet it. Find the best fillet radius by eyeballing (roughly, for outer radius less than 100 px, the best fillet radius might be anywhere in the range of 1 px to 15 px)