How to measure the max available online user amount per second?

How to measure the max available online us开发者_StackOverflow社区er amount per second for a web app using asp.net?

Is there any tool to measure that?

I am looking for load testing, to find out how many users my app can handle.

Is there any recommended load testing tool?

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Have you looked at the ASP.NET counters in Windows Performance Monitor?