The answer to 'what size air conditioner do I need for my house' is that the size of the air conditioner you need depends on the square footage of your home, the climate, and the insulation and efficiency of your home. As a general rule, you'll need about 20 BTUs (British Thermal Units) of cooling capacity per square foot of living space. So a 2,000 square foot home would typically need a 40,000 BTU air conditioner.
However, it's important to get an accurate calculation from a professional HVAC technician, as there are many other factors that can affect the right size, such as ceiling height, number of windows, shade, and insulation. Oversizing or undersizing an AC unit can lead to inefficiency, uneven cooling, and higher energy bills.