Apache JMeter can help to give an idea of how a server will perform when under very high load.
Install the latest version of Java
Next, download Apache JMeter
After unzipping the files, you'll go into the Apache JMeter directory, then the bin directory, and launch the program by running the file name ApacheJMeter.jar.
You'll be given a test plan to start with.
Add a thread group by right clicking on Test Plan, then Add, then Threads (User), then Thread Group.
Add an HTML request by right clicking on Thread Group, Add, Sampler, HTTP Request.
Add a graph so you can see the results. For this example we'll add a throughput graph. Right click on Thread Group, Add, Listener, Graph Results.
Go into the HTTP request, under Server Name or IP and add the full url that you are trying to test.
To change how many requests and how you want the test to go, open the Thread group section and modify it.
The loop count is either forever or a specific number of loops.
Once you are ready to get started, Click on Run, then Start.