The size of the mini-split for a garage depends on several factors, including the square footage, ceiling height, insulation, air escape through gaps and doors, and the climate in your region. According to a mini-split sizing chart, a 9,000 BTU mini-split is recommended for an average 1-car garage, a 12,000 BTU mini-split for a 2-car garage, and an 18,000 BTU mini-split for a 3-car garage. However, it is important to note that these are just general guidelines, and other factors such as the garages insulation and climate can affect the size needed. It is recommended to take measurements of the garage, calculate the area of the space, and determine the BTUs needed to choose the right size mini-split. If you are unsure of how to do this on your own, you can always contact a certified HVAC technician to help you determine the best size mini-split for your garage.