Collisions, collision avoidance, hidden terminals, and automatic rate selection in response to signal quality all reduce the effective bandwidth of the 802.11 wireless medium when many clients are active in proximity. To determine the resulting degraded bandwidth, experiments were conducted with 96 wireless clients operating simultaneously in a variety of signal quality conditions, each having traffic typical of a browser-interfaced Web service. The wireless medium was modeled as an M/M/1 queue with capacity a parameter determined by a nonlinear regression fit to the measurements. The analysis provides practical design guidelines for wireless bandwidth utilization and access point placement in settings having a large number of moving clients.