How to efficiently test the performance of a web application?

The web application I am currently testing is running on an apache2 server with a large chunk of html/css/js files. I have been mostly trying to test the

• load time


• Number of http requests (without data base64 encoded uri image requests which apparently add up to the total number of requests)


• Some information about the performance of JS scripts and Stylesheets


• ANY other useful information.

I have checked out this answer but I am looking for a free online tool which would give me more accurate analysis. I have been testing with

• Inspect Element


• http://ift.tt/vKAZ91


• loadimpact.com


• Several other online tools for testing

However, all of them give me different results even without cache. I mean, even the page size differs, not only the total requests, load time , etc. This makes me feel there must be something more efficient and accurate that I could use without paying a dime? Any suggestions would be helpful.