Rate As Answer, If you satisfied.
There is no fixed size for asp.net web page.
You can create page as responsive for each window size.
As per ur requirement u can use Hight and width of Website..
Generally we use the Width:100% and Hight:Auto.
U can use the same code as above and try it out..
But in general case developer prefer the mostly web page size near to screen size and most of case that will be approxe 1100*900.
Regards & thanks
So the size will be depends on customer choice..So we can say there
is no rule for the web page Hight and weith.