Understanding Concurrent Users
How we calculate. L ≈ λ × W — concurrency ≈ throughput × average response time. The form uses the same arithmetic as the worked examples on this page. See our methodology and accuracy policy.
Real-world scenario: A typical Concurrent Users case uses throughput (req/s) 200 and avg response time (seconds) 0.75. Enter the same figures below to reproduce the worked path.
What is Concurrent Users?
This estimates how many users (or in-flight requests) the system was handling on average. It assumes a roughly stable measurement window.
- Use the same window for throughput and response time
- Response time in seconds (convert ms ÷ 1000)
- Virtual users ≠ unique humans in many load tools
The Formula
Worked Example
Common Use Cases
- Load model design: size VUs from target TPS
- Bottleneck checks: compare estimated vs configured VUs
- Capacity planning: translate SLA latency into concurrency
Pro Tips
- Think time is outside W if you measure server response only
- Queueing spikes break steady-state assumptions
- Validate with tool concurrency gauges
Limitations: Concurrent Users figures are educational performance-testing aids—not contractual capacity guarantees. Validate with calibrated load tools and production telemetry.
FAQ
Is this exact?
It is an average-system estimate for stable periods, not a peak instantaneous count.
What about think time?
If users wait between clicks, include think time in W only when modeling end-to-end user presence—not pure server latency.
Authoritative References
For performance and quality engineering context, consult:
- ISTQB — performance testing syllabus topics
- W3C Navigation Timing — browser performance timing
- CMG / capacity forums — capacity and performance practice communities