Concurrent Users
IntermediateConcurrent users is the number of distinct people active on a site at one moment, counted in practice as the unique users seen in a short trailing window, usually five minutes.
The web protocol is stateless and no visitor stays connected to the server, so a truly instantaneous figure does not exist and what is reported is a window count. The window length is part of the definition rather than a side setting: on identical traffic a thirty-minute window returns several times the figure of a five-minute window, so comparing this metric across tools without knowing the window is meaningless. A name collision also causes recurring confusion: in server capacity planning and in licence agreements, concurrent users means simultaneous open sessions or purchased seats, not active visitors on a site. The common mistake is sizing infrastructure from the average of this number, when the only figure that matters for capacity is its peak.
How it is calculated
Concurrent users = number of unique users that sent at least one event within the short trailing time window
The window length must always be stated with the number, otherwise the figure cannot be interpreted. The unit is people and the count is recomputed continuously. The metric is not additive over time and summing the concurrent counts of successive minutes produces nothing meaningful; period comparisons should use the peak or the median of the range.