Align width of dropdown menu to?

In the past I ran often into the problem, that I did not know how to decide the width of a dropdown menu. I as a designer don’t mind to just eyeball a good-looking width, but developers would love to see some system behind it.

In the given example (google current) the width is 192px. The dropdown is actually wider than necessary. In other google products I have seen less wide dropdown menu. So it can’t be a minimum-width.

How do you guys set up width of objects like this?

I have the same problem with modals. Sometimes I see them super tiny and sometimes with lots of paddings.

Thanks!