Google Labs which is a part time project at Google, produces many long lasting products and sometimes just for fun materials. The latest addition to their long list of innovative tools is Browser Size, A tool which allows web developers and website owners, how many customers get the intended content without scrolling. For instance if you place a ad or a button in the bottom of the page, 30% of your users may never see the Ad/Button if they dont scroll.
It is basically a graph based on the Screen resolution of the web users collected by Google itself, in practical sense the tool may not show actual % for your site, rather it shows the Global Average. But still a nice tool to try and play with your websites.