How to calculate the number of concurrent users ? (Rule of 10-20%)

The number of users logged into the system is not the number of concurrency user. You should focus on the actual users processing /querying.

With the assumption that:

  • At any one time, 10-20% of your users will be logged in
  • Of those users logged in, only 10-20% will actually be running request (ie thread

You will rarely see concurrency go above 20% of logged user unless its specific to certain business processes (for instance Financial Management during a financial close period).

You will have with a total of 1000 users:

Number of concurrent users = 1000 x 0.2 x 0.2 = 40

These are general rule of thumb/guidelines. It is very difficult to suggest capacity planning recommendations without analysis of the expected usage.