Virtual User Calculators - Web Performance

Virtual User Calculators

Customers frequently ask us for help deciding how many virtual users they need for their load tests. We have a number of formulas for calculating this, depending on what information the customer has available. Last weekend I built online calculators for a few of the more popular variations. Give them a try!

If these don’t apply to the data you have available, contact us and we’ll be happy to help you calculate the number of simulated users required for your specific needs!


9 February 2012 myanees


I gone through the below link:

Please let me know the calculation formula of number of virtual users behind it.

9 February 2012 chris

The calculators are implemented in javascript. Take a look at the page source and you’ll find the name of the javascript file. You can then examine the source in that file to see the calculations.

17 April 2013 Sundar

Hi Chris.. I’m a fresher to Web performance load test tool.

When i run load test for 50 virtual users for a duration of 10 minutes, the user level gets stable at two instances, one at the 7 user mark and the other at 21 user mark. And the duration gets completed even without all the virtual users completing the load test. And consequently, load test report is generated for only 21 users (Maximum users analysed)

Could you suggest any procedure to deal this scenario?

17 April 2013 Chris


I can’t give very specific advice without seeing the test configuration and results. But if the VUs are not finishing the testcase, you need to increase the test duration.

For a more complete answer, I suggest submitting a support request using the Support Request wizard in the Help menu. If you include your test results with the request, one of our support engineers will be able to advise you.


18 April 2013 Sundar


I’ll seek advice from the support team for sure.

Just to let you know what i tried.
I tried a load test for 5 minutes, starting with an initial load of 25 users, then increasing by 10 users per minute (Limiting to 50 users)
At the end of 2 minutes, the 35 user mark was reached. Then for the remaining three minutes, no increase was seen with the user level remaining stable at 35 users till the completion of the test. The load test report shows 35 users as the maximum users analyzed. Also, User capacity is shown as 35.

Your comments on this?

Thanks in Advance.

18 April 2013 Chris

Load Tester will only add users to the engines if they have enough capacity available. It sounds like you have reached the capacity limit of the local load engine (which is built into the Load Tester UI). You can install stand-alone load engines on other computers to increase your capacity. Search for “load engines” in the help for instructions.


22 April 2013 Sundar

Thanks for your view, Chris.

Best Regards,

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