Window.UsableHeight (Word)

Returns the height (in points) of the active working area in the specified document window. Read-only Long.

If none of the working area is visible in the document window, UsableHeight returns 1. To determine the actual available height, subtract 1 from the UsableHeight value.

With ActiveDocument.ActiveWindow 
 MsgBox "Working area height = " _ 
 & .UsableHeight & vbLf _ 
 & "Working area width = " _ 
 & .UsableWidth 
End With