Measure the room area. Its length x width equals area. The bedroom in the house is 7 feet by 15 feet so the area is 105 square feet. Be guided by this recommedations.
I need at least a 5,000 BTU (British Thermal Unit) machine out there. My pre-bought Sanyo air conditioner is rated at 7,400 kJ/hour. That's 7,004 BTU's. Just make sure it's cleaned and filled up with freon.
cleaned and filled with freon after 2 years storage: Sanyo SA-76P