Most UniFi APs are capable of covering 1000-2000 ft2 (95-185m2). Given that walls and other obstacles may degrade signal, we generally recommend having at least one AP per 1000ft2 to maximize performance and connectivity.
Our WiFiman Mobile App (iOS/Android) is an excellent utility for optimizing your UniFi AP deployment. It demonstrates incredible utilities including WiFi speed tests, signal mapping, and even measures latency and throughput. We also recommend our UniFi Design Center for enterprise environments thanks to the unique ability to draw or upload floor plans and obtain WiFi coverage information.