Creating photos to use as ImageButtons in my app - regarding size

When creating images to place as ImageButtons in my app, what is the staple rule to go by in terms of width? I know each phone will resize accordingly with a wrap_content parameter, but what is the universal width I should be using? These are basic titles for eac开发者_开发问答h layout I am using, as reference.

Thanks!

Depends on what kind of icon you are creating (menu, app launcher, etc..). Icon sizes also depend on screen density.

Check out Icon Design Guidelines.