Screen sizes in pixels:
- iPhone 3GS 320x480
- iPhone 4 640x960
- iPad 1024x768
- iPad Retina 2048x1536
For a control to be “touchable” must at least have a 6x6 mm zone only for that control: in a 3GS iPhone is a about 44x44 px.
This doesn’t means that the control must have at least 44x44 px: means that no other control can be in that space: you can create a 1x1 button. And also it doesn’t mean that this size is a recommendation. This size is the minimal size for a touchable control, but is not a comfortable one.
Navigation bar height: 44 pixels Tab bar: 49 pixels