How to adjust the spacing around an icon in a button?

["Till Harbaum / Lists" <lists harbaum org>]

Hi,

i have buttons with icons inside. For some reason the button is slightly bigger than it needs to
be. Where do i adjust the border that's drawn around an icon in a button? Also this only affects
the height. Is there some kind of preferred vertical size of a button?

Regards,
  Till