Use Apache Benchmark (ab). It’s a command line tool that ships with apache web server. If you’re running *nix, chances are it’s already installed on your machine. For example, if you want to send 1000 requests to a web server running on localhost using 10 concurrent threads you would do this:
$ ab -n 1000 -c 10 http://localhost/
It’ll spit out a nice report giving you interesting stats such as requests per second, number of failures, and much more.