What size window air conditioner do I need?
Measure the room's length and width in feet.
How this is calculated
Method: ENERGY STAR's room-size chart (e.g. 100–150 sq ft = 5,000 BTU; 250–300 = 7,000; 450–550 = 12,000), then: −10% for heavy shade, +10% for strong sun, +600 BTU per person over 2, +4,000 BTU for a kitchen.
Assumptions: 8 ft ceilings and average insulation. High ceilings or poor insulation need more.
Frequently asked questions
Can an AC be too big?
Yes. An oversized unit cools quickly but shuts off before removing humidity, leaving the room cold and clammy.
How many square feet does 8,000 BTU cool?
About 300–350 sq ft under the ENERGY STAR chart.
How many BTU for a 12×12 bedroom?
144 sq ft falls in the 5,000 BTU range.
Do I count the hallway?
Only if it is open to the room and you want it cooled.