Work out little law concurrency instantly with clear inputs, formula shown and shareable results.
Little's law states L = lambda x W for any stable system, with no assumptions about arrival or service distributions. That makes it a consistency check: if observed concurrency does not match arrival rate times measured latency, one of the three measurements is wrong — usually because latency is measured at a different point than arrivals, or because the system is not actually stable.
Little's law
L = lambda x W; equivalently W = L / lambda and lambda = L / W
Yes, that is the only assumption. Over a window where arrivals roughly equal departures it holds exactly, regardless of the distributions involved.
If concurrency is far above lambda x W, requests are being held somewhere your latency metric does not cover — often a queue ahead of the instrumented code.