To help webmasters understand how everyone sees their websites, Google created a brand new tool called Browser Size, and its live today. Browser Size is based on a sample of data from visitors to google.com. Special code collects data on the height and width of the browser for a sample of users. For a given point in the browser, the tool will tell you what percentage of users can see it. For example, if an important button is in the 80% region it means that 20% of users have to scroll in order to see it. If you’re a web designer, you can use Browser Size to redesign your page to minimize scrolling and make sure that the important parts of the page are always prominent to your audience. We hope people will use this tool to make their websites better, in turn making the web better for everyone.

To make it work, just go to this page and enter your site URL there, then it will show you in percentage how many viewers see the website at different resolutions. The data is visually displayed and is easy to understand.

google-browser-size

Google code blog has more details on this tool.