The cooling capacity of an air conditioner is typically measured in British Thermal Units (BTUs) per hour. A 9,000 BTU air conditioner is generally suitable for cooling a room with an area between 300 to 400 square feet (28 to 37 square meters). However, it's important to consider various factors that can affect cooling requirements, such as room insulation, ceiling height, number of windows, local climate, and heat-generating appliances or electronics. It's recommended to consult the manufacturer's guidelines or seek assistance from an HVAC professional to determine the appropriate cooling capacity for a specific room or space.