Hi, I am executing the following javascript on my browser(firefox) 1.console.debug("Screen height = "+ screen.availHeight); //output 770 2.console.debug("Window Height ="+ $(window).height()); //output 210 (i am using jQuery as well) What is the difference between the two? Are units of 770 is pixels and 210 is mm ? Similarly, when I write $(document).height() and $(window).height() , there is a difference . What is the reason ?