The cooling capacity of an air conditioner is typically measured in British Thermal Units (BTUs) per hour. A 12,000 BTU air conditioner is generally suitable for cooling an area of about 350 to 550 square feet (32 to 51 square meters) in size. However, it's important to consider various factors such as insulation, ceiling height, sunlight exposure, and the number of occupants or heat-generating appliances in the area. These factors can influence the cooling capacity needed for a specific space. It's recommended to consult the manufacturer's specifications or seek professional advice to determine the appropriate cooling capacity for your particular circumstances.