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How to Calculate the Number of VUsers

Is there a rule to determine the number of VUsers given the number of human users hitting a website (let's say within a one hour time frame)? Other variables may be how long the average use visits the website.

For example a website that 500 end users may visit in a one hour interval and each user browses for 5 min. What would be the number of VUsers required?

Also, if I was to specify say 15 VUsers for a scenario, how many end users does that represent?

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Re: How to Calculate the Number of VUsers

Hi Rob,

If you want to use vusers to simulate the load of real users, make sure set proper think time in the script, the time that costs to run the script for 1 iteration should be almost the same as the time cost by manual operation. If you want to simulate 500 real users, just run 500 vusers.

here is an example: duration: 1 hour, 500 vusers, suppose 1 interation costs 30 seconds, 1 user browses for 5 mins, so it's 10 interations for each vusers. The pacing(break between each interaction) should be 5.5 mins.

If think time is enable during load test, one vuser represents one real user, if think time is disabled one vuser represents about 5 real users.

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Re: How to Calculate the Number of VUsers

A single vuser represents a single human user, so if you want to check whether your application will withstand X users accessing it concurrently, you need to create a test with X vusers running together at the peak of the load.

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Re: How to Calculate the Number of VUsers

See attached.

I have this excel for every Business Processes we test.

You enter:

- Column G: The Runtime of the script in seconds (This will change under load so I generally enter the time it takes in VuGen, then update after the first run) - BP5 has 5min (300 sec) for your case.
- Column I: What throughput of each scenario is required/hour - 500 in your case.
- Column L: Number of users per BP.

I have Column M and N automatically updating, with a formula which I have shown on row 8, based on the above and

- Column M: Iterations that each user will run (not really interested in this)
- Column N: We will enter this into the pacing in the run-time settings of the script.

Then I update the Number of users (Column L) until the Pacing is positive.

In my example, attached, I left BP01 pacing as -2 - which means that I don't have sufficient users to complete 500 iterations if the scripts takes 60 seconds to run... so i would update that to 9 users.

I keep an eye on the "Total Users" as well incase that's a limiting factor on licensing.

Hope this isn't too confusing.

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Re: How to Calculate the Number of VUsers

>> "Also, if I was to specify say 15 VUsers for a scenario, how many end users does that represent?"

Ideally, 15. Try to configure your scripts and scenarios so that they mirror actual users as much as possible. There are some cheats and exceptions to this. But for the most part, try to make them realistic.