Virtual User Calculator

What is the Virtual User Calculator?

The Virtual User Calculator tells you how many concurrent virtual users (JMeter threads, LoadRunner Vusers, k6 VUs) you need to configure so that your load test produces a target throughput. Instead of guessing a user count and adjusting it run after run, you enter the transactions per second the system must handle along with your script’s response time, think time and pacing, and get the concurrency required to hit that load.

How it works

Little's Law connects throughput and concurrency: the number of virtual users you need is the target throughput multiplied by the average time each user spends in the system per iteration (response time, plus any think time and pacing you've configured).

Formula to calculate virtual users

Where:

• Target TPS — Transactions per second the system must sustain.
• Response Time — Average time to complete one transaction, in seconds.
• Think Time — Delay a user takes before the next action, in seconds (0 if none).
• Pacing — Wait time between two iterations, in seconds (0 if none).

Example of virtual user calculation

An e-commerce checkout API must handle 50 transactions per second during peak hours.

Inputs

• Target TPS = 50
• Response Time = 2 seconds
• Think Time = 3 seconds
• Pacing = 0 seconds

Step-by-step

1. Time each user spends per transaction = 2 + 3 + 0 = 5 seconds
2. Virtual Users = 50 × 5 = 250

Common mistakes to avoid

• Forgetting to include think time — this understates the number of virtual users needed and under-loads the system under test.

• Using peak response time instead of average response time, which overestimates the required concurrency.

• Confusing "virtual users" with "requests per second" — they measure different things and this calculator converts between them.