What Size AC Do I Need for My Room?
Sizing is a heat-load calculation, not a guess from floor area alone — and both undersizing and oversizing cause problems.
What BTU means
BTU ratings describe cooling capacity. Common domestic sizes run from around 9,000 BTU for small bedrooms up to 24,000 BTU and above for large or open-plan spaces.
Beyond floor area
Ceiling height, glazing area and orientation, roof construction, occupancy, kitchen or equipment heat and how well the room is sealed all change the required capacity.
The cost of getting it wrong
Undersized units run continuously and never satisfy the room. Oversized units short-cycle, leaving the space cold and humid, and wear the compressor.