Load Testing Calculators
How Many Virtual Users Do I Need?
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One of the most common questions we get is "how many virtual users do I need to simulate?" The obvious answer is "how many people do you expect to have accessing the your system simultaneously?". If you have this information, then you're done!
But a tester or project manager frequently has less specific information available, such as stats from a web log analyzer. The calculators on this page will help determine how many virtual users are required to accurately simulate the expected load on a website.
Peak Hourly Visits and Average Visit Length
If you know the peak hourly visit rate (the number of unique visitors to the website in its busiest hour) and the average visit length (the amount of time, on average, each use spends on the website), enter them below for an estimate of the required Virtual User count.
Peak Hourly Pages, Testcase Size and Duration
If you know the peak hourly page rate (the number of pages visited on the website in its busiest hour) and the size and duration of the testcase (number of pages and duration in minutes), enter them below for an estimate of the required Virtual User count.
How Many Rows of Data Do I Need?
It's common for datasets to consist of data is only useable once per test. For example, you might be logging in as a user, completing and submitting a one-time form, and logging out. In such a case, you'll need to calculate how many rows of data you'll need over the course of the test. Also, you'll need enough data so that when it's split up amongst the load engines, each load engine has enough data to avoid running out if the load engines are slightly unbalanced.
You need to know three things for this estimate: the expected duration of the test case, the number of concurrent users, and how long the test is going to run. This calculator assumes a steady ramp for the duration of the test: if you need to ramp more quickly and then hold at a level for a longer period of time, calculate the rows of data necessary for the ramp period first, then for the load period. For details on the calculations, refer to this blog post.
Note that this calculator does not take into account dataset rows with a lifetime shorter than "test case" - if you're using multiple data rows per test case iteration, simply multiply the below results by the number of rows in use per test case. Also, if you expect some errors, then pad the dataset to account for those test cases terminating early.
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About
Christopher L Merrill
©2009 Web Performance, Inc.
