Based on their British thermal unit capacities, portable air conditioners can cool rooms of various sizes. Each square foot of a room requires approximately 33 BTUs to cool, so a portable air conditioner with 5,000 BTUs can cool a room that is 100 to 150 square feet.
A higher-capacity portable air conditioner with 12,000 BTUs can cool a room that is 450 to 550 square feet. A very sunny room requires a portable air conditioner with a BTU capacity 10 percent higher than under regular circumstances. Cooling a kitchen requires 4,000 more BTUs than is normally be needed for the same square feet of space.