How can I determine number pixel in resolution?

to get the resolution in twips:

screen.twipsperpixelx
screen.twipsperpixely

to get the screen size in pixels and /or mm:

Declare Function GetDeviceCaps Lib "gdi32" _
    (ByVal hdc As Long, ByVal nIndex As Long) As Long

with Index:

Public Const HORZRES = 8 ' Horizontal width in pixels
Public Const HORZSIZE = 4 ' Horizontal size in millimeters
Public Const VERTRES = 10 ' Vertical width in pixels
Public Const VERTSIZE = 6 ' Vertical size in millimeters

Marco