GT Metrix http://gtmetrix.com is good online free service to check you page response time. It works on grading of response time you should always try to achieve at least A . This service not only tells you response time but it also tells you factors which are causing slow response time .Now I am going to show you how to use this service
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Type your URL of page here click GO and Wait
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After processing your request it will show u a report like the one below.
As You can see in image there are many factors which are slowing response like GZIP compression not enabled on server , Images are optimized on browser and it’s also giving them priority fixing these issues will cause increase in performance
Software Testing Tools and Techniques 