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Little's Law Calculator

Free Little's Law calculator (L = λW). Solve for concurrency, throughput, or latency from the other two — for sizing connection pools, thread pools and load tests.

Result—

The law

L = λ × W

L = average concurrency (requests in flight)
λ = throughput (requests per second)
W = average latency (seconds)

It holds for any stable system regardless of traffic distribution. Given any two of the three quantities, the third is fixed — which makes it the fastest sanity check in capacity planning.

What it's good for

  • Sizing pools. Required concurrency = throughput × latency tells you the minimum connection/thread pool size to avoid queueing.
  • Load test design. The virtual-user count to hit a target throughput is λ × W — the same math behind the pacing calculator.
  • Spotting ceilings. If your pool is smaller than λ × W, throughput is capped no matter how fast the backend is.

Full walkthrough: Little's Law for performance engineers. It speaks to averages, not the tail — pair it with the percentile analyser.

Discussions coming soon.

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