What size air conditioner do I need?

How air conditioner sizing works

Air conditioners are rated in BTUs. Start at roughly 20 BTU per square foot, then adjust: add ~10% for a very sunny room, subtract ~10% for heavy shade, add 600 BTU for each person beyond two, and add 4,000 BTU if it’s a kitchen. Oversizing is a real mistake — an AC that’s too big cools fast but leaves the room clammy because it never runs long enough to pull out humidity.