True size of a MovieClip that contains a masked clip

Hello there,
I just want to know if there is a way to obtain width and height of a DisplayObject based on what the user sees on the screen.
Imagine a MovieClip with inside a clip that masks (for example) another much-more-bigger-clip.
If I ask the width or the height of this clip, at runtime Flash reports the width and the height of the much-more-bigger-clip while I would have needed only the visible part.
Thanks in advance and sorry for my english, I hope you have understood what I have written.