You can use the InsideHeight and InsideWidth properties to determine the height and width (in twips) of the window containing a form.
Setting
The InsideHeight and InsideWidth properties are available only by using a macro or Visual Basic and can be set at any time.
Remarks
If you want to determine the interior dimensions of the form itself, you use the Width property to determine the form width and the sum of the heights of the form's visible sections to determine its height (the Height property applies only to form sections, not to forms). The interior of a form is the region inside the form, excluding the scroll bars and the record selectors.
You can also use the WindowHeight and WindowWidth properties to determine the height and width of the window containing a form.
If a window is maximized, setting these properties doesn't have any effect until the window is restored to its normal size.