Web Concurrency, QPS and Latency: Estimate Capacity Carefully
Web concurrency is the amount of work in flight; QPS is requests processed per second. They are not interchangeable. Daily page views alone cannot tell you how much concurrency a service must support, because request patterns and response times matter.
Keep the units explicit Metric Meaning QPS Requests per second at the measured boundary. TPS Transactions per second; define what constitutes a transaction. In-flight requests Requests started but not yet completed. Latency Time a request takes; inspect percentiles as well as averages. Page views A browsing measure that may generate several backend requests per view. For a stable system, a useful approximation is average in-flight requests = request rate × average response time. With 100 requests/second and 0.2 seconds per request, the average is about 20 in flight. This is an estimate, not a promise about peak queues or tail latency.
