We describe an analytical process to determine how much UAS traffic is feasible. The process is a simulator and data processing tools. The two are applied to the US San Francisco Bay Area and Norrkoping, Sweden. The amount of UAS traffic is measured in flights per day and simulated up to 200,000 flights. A UAS traffic volume is feasible if specified metrics meet operational requirements with high probability and are stable, in the sense of being below thresholds observed for monotone properties in random geometric graphs. We focus on conflict cluster size and argue for it as a fundamental safety metric worthy of extraordinary consideration.