Getting the correct pixle size of a button on VC++6.0 for icon creation

what i intent to do is to design a picture for my button instead of using text. But i need sizing. On VC++6.0, using the visual editor, when i highlight the button, it gives me the size at the bottom right corner of the screen ( as well as the position)

It says 100 x 100
Using this size, i created an image of 100 x 100 pixle but unforturnately it doesnt fit exactly onto the button. it's too small!! So i conclude that 100 x 100 isnt exactly the pixle size of the button but something else. So how do I get a correct pixle sizing of the button so i can create an image??

Using
- win98se
- VC++6.0
- API style

GetDialogBaseUnits()
MapDialogRect()

gg