Please forgive my lack of understanding on this subject. I had bunch of urls that I am interested to know the size of its web page. So, I used HTTP Head req method to get the Content-Length. I verified the Content-Length values generated from Head method by opening some of those urls in a browser (I used Firefox) and checking the "View Page Info" (from right-click on website in browser) option that gives the "Size:".
For most of the urls, both the values matches but not for some. I wonder why is that?