Google recently added a features over its Webmaster Tools to check out your site speed for the better performance of your site. They have discussed on their forum about it :
"We bring data and statistics specifically applicable to your site. On Site Performance, you’ll find how fast your pages load, how they’ve fared over time, how your site’s load time compares to that of other sites, examples of specific pages and their actual page load times, and Page Speed suggestions that can help reduce user-perceived latency. Our goal is to bring you specific and actionable speed information backed by data, so stay tuned for more of this in the future."