How to find width of a menubar?

["Sudrien" <sudrien fusemail com>]

I have a menubar in a toolbar item, with buttons on either side. I have no
idea how wide this menu will be, and I find if it gets too wide,  first
the buttons go into an overflow menu, and then the menubar dissapears
altogether.

If I knew the width of the menubar, I could modify its contents so
everything stays visable.

How could I do that? How could I check the width it will be rendered at?

-Sud.